Alkyd Drying

9Paints, Varnishes,

and Related Products

K. F. Lin

1. RELATIONSHIP OF FATS AND OILSTO THE PAINT-COATING INDUSTRY

Historically, drying oils have been the major film formers of coatings, including

paints, varnishes, and inks. Although it is not certain whether linseed oil was

used in paints in ancient Egypt, flax was grown and flax seeds were collected at

that time. The early Renaissance was probably the real beginning of paints as we

know them today in the West. The Van Eyck brothers (1388–1441) are said to be

the first to use linseed oil as a binder (1). Whereas in China, tung oil has been used

for centuries as waterproofing caulking or as coating for wood objects including

boats, houses, and furniture.

The first American paint factory was opened in Boston in 1737 by Thomas

Childs (2). The pigment and oil were placed on a granite trough, and a granite

ball, known as the Boston Stone, was then rolled over the mixture to make the paint.

The ball is now preserved and serves as the symbol for the Federation of Societies

for Paint Technology.

The drying oils owe their value as raw materials for decorative and protective

coatings to their ability to polymerize and cross-link, or ‘‘dry,’’ after they have been

applied to a surface, to form tough, adherent, impervious, and abrasion-resistant

Bailey’s Industrial Oil and Fat Products, Sixth Edition, Six Volume Set.Edited by Fereidoon Shahidi. Copyright # 2005 John Wiley & Sons, Inc.

307

films. Their film-forming properties are closely related to their degree of unsatura-

tion, since it is through the unsaturated centers or double bonds that polymerization

and cross-linking take place. With one exception (to be noted later) the oils used

in paints varnishes and similar products are relatively high in iodine value. In any

given product, there is an optimum degree of reactivity in the oil; the speed with

which the oil dries must be balanced against such factors as elasticity and durability

in the paint film. In general, however, unsaturation is at a premium in paint and

varnish oils, and the oils in greatest demand are those in which drying takes place

most readily.

The form in which drying oils are used in coating applications has gone

through an evolutionary change over time. The simplest and most primitive

way is to use them directly as the film former of a coating. It was discovered that

drying oils may be made more useful by altering their natural state. By aging

in vats, by heating, or by blowing air through, the viscosity and drying character-

istics of the drying oil may be changed enough to improve its general properties for

coating applications. In the case of fast-drying oils with conjugated double bonds,

such as tung, oiticica, and dehydrated castor oil, heat treatment is necessary to

‘‘gas-proof’’ them, so that the oils do not dry into undesirable wrinked and/or

frosted films. The oils are not necessarily used in their original form of triglycerides

for coating applications. It has become a common practice to hydrolyze them first,

and the free fatty acids are then used to synthesize coating resins with certain advan-

tages. Therefore, the term fats and oils includes fatty acids for the purpose of the

discussions in this Chapter, unless otherwise specified. Through progress, people

found that sometimes mixtures of different oils could be used to greater advantage

and that natural gums could be added; thus oleoresinous varnishes were born.

Thereafter, human creativity started to make rapid and diversed progress in the

development of new coating materials, many of which have departed completely

away from the drying oil base.

When the drying characteristics of oils were relied on as the sole (or major) cause

for a varnish-based coating film to dry, those oils belonging to the linolenic or con-

jugated acid groups, such as linseed, perilla, tung, oiticica, and highly unsaturated

winterized fish oils were of the prime interest to coating formulators. Since about

the 1950s, with the advent of synthetic resins, particularly, alkyd resins, it has

become possible to make considerable use of oils with poorer drying character-

istics. Semidrying oils such as soybean oil, safflower oil, and sunflower seed oil

have become viable as raw materials for making ‘‘drying’’ paints. Nondrying oils,

such as coconut oil, are also used in coating materials. However, their function is

primarily that of a plasticizer rather than of an active component for air drying. In

addition, castor oil, a nondrying oil, has been converted chemically by dehydration

to give excellent drying property.

There is no denying that the once prominent position of fats and oils as the most

important raw material for coatings has been greatly eroded by other materials. The

total U.S. consumption of drying and semidrying oils in coating and allied applica-

tions peaked around 1950 at about 1.2 billion lb. It went down steadily thereafter.

According to SRI International (3), the direct use of drying oils accounted for only

308 PAINTS, VARNISHES, AND RELATED PRODUCTS

about 4% of the total film formers consumed in the United States in 1990, at about

98 million lb, whereas the consumption of alkyds, urethane alkyds, and epoxy esters

was estimated at 645, 40, and 12 million lb, respectively (4–6). Very little drying oil

is used in paints at present. Drying oils and oxidizing alkyds have been studied as

binders for organic inorganic coatings (4). Urethane coatings are the fastest growing

sector. Use in 2003 was 1:6� 106t (5). Epoxy resins are among the most widely

used (6).

2. A BRIEF OVERVIEW OF THE COATINGS TECHNOLOGY

Modern requirements in protective coatings are extremely diverse and exacting.

They go far beyond the mere necessity of protecting the finished surface from

weather or from ordinary wear or abrasion. Some coatings (e.g., those employed

as electrical insulation) must possess extreme resistance to high temperatures or

to penetration by moisture. Others (e.g., marine varnishes and the enamels for coat-

ing the interior of cans) must withstand prolonged contact with water or aqueous

solutions. Modern assembly-line methods of manufacture produce many particular

requirements and have created a special demand for quick-drying finishes. The wide

distribution of illustrated journals, the proliferation of advertising matter, and the

development of high speed printing processes have greatly elaborated the require-

ments of users of printing inks. Tung and other conjugated oils are particularly

suitable for manufacture of fast-drying finishes, and for a time, the consumption

of these oils increased significantly in response to more exacting requirements

for specialized finishes. New systems based on epoxy resins, urethane polymers,

silicones, and other synthetic intermediates have greatly decreased dependency on

tung oil, and use has shrunk significantly.

The complex and diversified requirements of modern industry have to a large

extent removed the manufacture of paints and varnishes from the category of an

art to that of a science. In most plants, the manufacturing processes are now carried

out under careful laboratory control and are freely modified or revised, whenever

revision is indicated, in accordance with known scientific principles. As a result, the

industry has been able to offer a succession of constantly improved products through

periods of fluctuation in the availability of many important raw materials, pressures

for solvent replacement to meet emerging air quality standards, and extensive pig-

ment reformulation to replace mercury and lead to conform to new federal regu-

lations on toxicity.

A most important development in the modern paint and varnish industry has

been the introduction of synthetic resins as replacements for natural resins in the

manufacture of varnishes and enamels. By using synthetic resins it has been pos-

sible to produce a variety of coatings that, in many cases, have important points

of superiority over any of those compounded from natural resins. The synthetic

vehicles are particularly distinguished by their hardness and durability and their

high degree of resistance to the action of water, alkalies, and other chemical

agents.

A BRIEF OVERVIEW OF THE COATINGS TECHNOLOGY 309

New methods for application of paint films and new procedures for curing have

placed challenging demands on the resourcefulness of the resin chemist. For years

brushing was virtually the only method of application; later, spraying, was used.

Now a host of new application and curing techniques are commonplace. These

include roller coating, dipping, coil coating, powder coating, electrodeposition, hot

spray, fluid bed coating, electrostatic spray, two-component spray, ultraviolet

cure, and electron beam cure.

The two foremost reasons for the decline of the direct use of oils, including

oleoresinous varnishes, for coating applications are performance and environment.

Drying oils by themselves, or even in the form of oleoresinous varnishes, do not

give the drying speed and, sometimes, film properties that would satisfy the modern

needs. The ease in the application and cleaning of latex paints caused oil-based

paint to lose most, if not all, of the trade-sales market. The implementation of

Rule 66 in California was the opening salvo for protecting the environment against

solvent-based coatings of which practically all oil-based coatings belong. Thus the

emphasis has switched to the development and commercialization of other coating

materials or systems that are more environment friendly than oil-based materials.

Indeed, it is quite remarkable that in the face of such severe odds, oil-based mater-

ials have been able to hold ground as well as they have.

There is an extraordinary body of terms used to define various features of pro-

tective coatings. Before discussing paints and varnishes and the particular function

of fats and oils in coatings, it is desirable to review and define some of the language

of the industry.

Protective coatings protect (or decorate) surfaces. Greases, mineral oils, plastic

web coats, and mastic compositions may be used for protection, particularly of

metal surfaces; but in the usual sense, protective coatings are materials that form

durable films adhered to the surface to provide protection.

A varnish is a solvent-thinned combination of a drying oil and a hard resin. Also,

a varnish is the clear film obtained using a varnish as a coating vehicle. By exten-

sion, vehicles used for clear films are called varnishes although the vehicle may be a

true varnish, an alkyd resin solution, a urethane-modified oil, or even a lacquer.

A paint is a pigmented system applied to hide and protect a surface. Paints con-

tain a wide range of ingredients as follows:

The vehicle is the carrier for pigment, consisting of combinations of oils, resins,

polymers, and solvents; the nonvolatile portion is commonly called the binder.

Prime pigments are used for their ability to hide or cover the surface. The term

hiding power is used to describe the relative ability of fixed amounts of

different pigments to cover a surface and depends on the difference in

refractive indices between the pigment and the binder; thus primary pigments

usually have high values in refractive index.

Extender pigments give relatively little hiding, but their cost is lower than that of

prime pigments; they provide control of such properties as flow consistency,

durability, and adhesion.


Driers are metal salts, especially of cobalt, manganese, zirconium, calcium, and

iron, that accelerate the conversion of the liquid film to a solid; lead was

commonly used as a primary drier, but due to its toxicity, it is rarely used

now.

Solvents or thinners control paint consistency and application properties. Slow

solvents evaporate slowly and leave the film ‘‘open’’ (workable) for longer

periods than fast solvents, which evaporate rapidly; in water-thinned paints,

water is the thinner and there is no control over rate of evaporation.

A variety of other materials may be added for special effects.

Antiskin agents minimize skin formation on the top of the can during use or

storage.

Mildewcides protect the applied film from fungus growth.

Wetting agents or griding aids promote wetting of pigment particles by the

vehicle.

Antiflood and antifloat agents minimize flooding and floating, deficiencies

characterized by separation of colored pigments during drying.

Antisetting agents minimize separation of pigment into a firm or hard mass in

the bottom of the can.

Antisag agents minimize sagging or ‘‘curtaining’’ of wet films during application.

Puffing agents, or thixotropic agents, increase the paint consistency and mini-

mize sagging by giving a thixotropic consistency to paint (a type of behavior

in which the viscosity of the system decreases when agitated, as under the

shear of brushing, and increases when allowed to stand).

Paints are made by grinding pigments in the vehicle. Actually the term grinding

is somewhat inaccurate. The pigments are received from the manufacturer are

already as fine in particle size as they will be in the finished paint. The grinding

operation is designed to break up the aggregates of pigment particles and to dis-

perse them in the vehicle so that each particle is wetted. Griding is usually carried

out in roller mills, in which shear between steel rollers disperses pigments, in ball

mills or pebble mills, in which steel balls or pebbles rotating and rubbing against

each other in a closed cylinder to produce the shear for dispersing the pigment, or in

sand mills, in which agitation of sand causes pigment separation and dispersion. For

products in which a fine grind (fine pigment dispersion) is not required, as in barn

paints or house paints, high speed rotors may be used to grind the paint. In typical

paint manufacture, a paste prepared from all of the pigment and a portion of the

vehicle is subjected to the appropriate grinding technique until the desired fineness

of grind is attained, and the resultant paste is ‘‘let down’’ (diluted) with the remain-

ing portion of vehicle and solvent.

Fineness of grind is commonly expressed numerically using a grind gauge,

which is a shallow wedge cut from polished metal. Paint is filled into the wedge


and a bar is drawn across the surface. With fine grinds, the paint fills the wedge even

to the shallowest part. With coarse grinds, the paint is pulled away from the shallow

edge of the wedge of the deeper end. The line of demarcation ranging from 0

(very coarse grind) to 8 (ultrafine grind) designated the quality of the pigment

dispersion.

An enamel is a paint based on a vehicle that dries to a considerably harder film

than paints derived from unmodified drying oils. Paints and enamels are classified

by type of finish as follows:

Flat paints or enamels dry to a velvety nonglossy or matte surface.

Semigloss paints or enamels dry to an intermediate gloss range between flat and

glossy.

Gloss paints or enamels dry to a highly reflecting surface.

There are many variations in the nomenclature, and films that are called gloss

films by one observer might be classified as a semigloss by the individual who

demands mirrorlike surfaces. Other designations might be used also such as egg-

shell (between flat and semigloss) or full gloss to differentiate mirror gloss from

normal gloss.

The degree of gloss is measured by a glossmeter, which measures light reflec-

tance at a low angle from the horizontal (20� gloss) or high angle (60� gloss). The

60� reflectance is most common, and although ranges of values are not sharply

divided, the general consensus is as follows:

Since the ability of a surface to reflect light, which gives the gloss measurement,

depends on the smoothness of the surface, one can readily visualize that a coating

with a greater surplus of binder over its pigment content will have a greater ability

to produce a smooth surface, thus high in gloss. Conversely, with a high pigment

content, there will be more pigment particles or aggregates at or near the film sur-

face to cause a scattering of light, thus resulting in low gloss. The amount of pig-

ment in the paint is measured by the pigment volume concentration (PVC), i.e., the

volume percent of pigments in the dried paint film. In solvent-based systems,

products of low PVC (up to 20–25%) are glossy, products in the middle range

Type of Paint 60� Reflectance

Flat 4 or 5 maximum

Eggshell 5–20

Semigloss 20–60 (up to 80)

Low gloss 80 to 90þHigh or full gloss 90 to 98þ


(25–50%) have a semigloss finish, and products in the high range (45–70) have a

flat or matte surface. Gloss in water-thinned systems does not correspond to the

above, particularly in emulsion systems, because the pigment particles are not

wetted uniformly by the binder. Solvent-thinned paints containing certain ‘‘flatting

agents’’ such as extremely fine silica do not conform to the normal pattern.

Coating systems are divided into two general classifications, depending on the

point of application. Trade sales finishes are purchased by the user in a paint store

or hardware store (or today even in a drugstore or a supermarket) and are applied by

the purchaser, usually by brush or roller. Included are barn paints, house paints, trim

paints, varnishes, porch and deck enamels; wall paints, architectural enamels, and

similar user-applied finishes. Industrial finishes are applied to objects by the manu-

facturer, usually by spraying, dipping, roller coating, air knife, or other high speed

production application methods, and they are usually force dried by baking. Imple-

ment, automotive, appliance, and furniture finishes are typical industrials.

Finishes are also described by the function of the paint. A primer is used to coat

the original surface. Its major functional property is good adhesion. Protection

against corrosion is an especially important characteristic of metal primers. Hiding

is a secondary function.

A sealer is a primer whose major function is covering a porous surface such as

plaster, gypsum board, or paperboard with a surface coating that exhibits a mini-

mum penetration into the surface. Good sealing prevents ‘‘ghosting,’’ a film defect

in which variation in penetration causes gloss differences and visual color differ-

ences in the final coat. A typical ghosting effect is obtained in painting wallpaper

in which the pattern can show through multiple coats because of the variability in

porosity of the substrate.

A sanding sealer is designed for easy sanding after short dry so that smoother top

coats can be attained. Sanding sealers are most important in furniture finishes and

industrial finishes such as automotive systems.

An undercoat is another name for primer or sealer, especially as an enamel

undercoat, which serves to supply a uniform base for an enamel so that there

will not be a wide variation in gloss. Undercoats may be applied over sealers.

The top coat or finish coat is the outside layer of paint applied over the primer

or sealer.

The specification of products for coating applications involves a large number of

factors, including color and color retention of films, rate of setup, bakability, rate of

cure of films, hardness of films, adhesion, wetting action in grinding with pigments,

flexibility and retention of flexibility on aging, reactivity with pigments, reactivity

with driers, water resistance, alkali resistance, solvent resistance, viscosity, visco-

sity stability in the package as clear products or in pigmented systems, thermo-

plasticity, durability, compatibility with other film-forming agents, mar resistance,

abrasion resistance, stain resistance, performance in the varnish kettle, gloss, gloss

retention, etc. Obviously, no single product can be optimum in all of these character-

istics, and in each use a compromise must be made to provide the best performance

in the intended usage.


3. FILM DRYING PROCESS OF OIL-BASEDCOATING MATERIALS

3.1. Drying of a Nonconjugated System

As mentioned earlier, it is through the unsaturated centers or double bonds of the

fatty acids in drying oils that polymerization and cross-linking, i.e., drying, takes

place. Hence, oils are conventionally classified, based on their iodine values into

three groups: drying, semidrying, and nondrying. The generally accepted demarca-

tions are, respectively, >140, 140–125, and <125. These numbers are, more or less,

arbitrarily assigned. When the oil contains conjugated double bonds, the iodine

values determined are usually low due to incomplete halogen absorption. Such a

classification can only be used for a rough guidance.

Wicks and Jones (7) suggested that the methylene groups between two double

bonds, i.e., the CH2 groups allylic to two C��C groups, are much more reactive than

those being allylic to only one C��C group and are mostly responsible for the dry-

ing of the nonconjugated oil. Thus the average number of such groups fn in an oil

molecule serves as a better indicator for the drying characteristics of the oil. An oil

with an fn value of greater than 2.2 is a drying oil, those with fn values somewhat

less than 2.2 are semidrying, and there is no sharp dividing composition between

semidrying and nondrying oils, according to the authors. While such a classification

system does have merits over the conventional way (based on iodine value), it does

not provide a ‘‘rule’’ for classifying oils with conjugated unsaturation.

The chemical mechanism of drying has been established as an oxidative radical

chain reaction process, which has been summarized as follows (8):

1. A period of induction at the beginning of the reaction during which no visible

change in physical or chemical properties in the oil is noticed; natural

antioxidant compounds are consumed during this period.

2. The reaction becomes perceptible and oxygen uptake is considerable; discrete

interaction of oxygen and olefins takes place followed by the formation of

hydroperoxides.

3. Conjugation of double bonds occurs accompanied by isomerization of cis to

trans unsaturation.

4. The hydroperoxides start to decompose to form a high free-radical concen-

tration; the reaction becomes autocatalytic.

5. Polymerization and scission reactions begin and yield high molecular weight

cross-linked products and low molecular weight carbonyl and hydroxy

compounds; carbon dioxide and water are also formed and are present in

the volatile products of film formation.

It is now generally believed that the induction is slow at first but is autocatalytic

and the rate increases steadily. The rate depends on the reaction conditions such as

temperature, light, and traces of heavy metals or inhibitors in the oil or coating (9).


The active sites are the allylic carbon a to a double bond, especially those a to

two double bonds with one on each side, such as carbon number 11 in a 9,12-octa-

decadienoic (linoleic) acid and proceeds through the following mechanism:

CH CH CH2 CH CH

−H

CH CH CH CH CHCH CH CH CH CHCH CH CH CH CH

O2

CH CH CH CH CH

OO

CH CH CH CH CH

OO

CH CH CH CH CH

OO

H

CH CH CH CH CH

OOH

CH CH CH CH CH

OOH

CH CH CH CH CH

OOH

Abstraction of a hydrogen atom

Resonance hybrid free radicals

Three possible peroxy radicals

Addition of hydrogen atom abstractedfrom another linoleate molecule

Three possible hydroperoxides, two ofwhich are conjugated

The initial step is believed to be the dehydrogenation from the a-methylene group

to form a radical. Since such a hydrogen extraction would require a considerable

amount of energy, a number of investigators proposed that the hydrogen is removed

through reaction with a free radical. Thus a radical, A � , abstracts a hydrogen from a

molecule of linoleate, RH, to form the radical R � ,

RHþ A� ! R � þAH

Since the radical is allylic to the double bonds on either side of it, resonance hybrid

free radicals are formed resulting in shifting the double bonds to a conjugated posi-

tion. This is then followed by:

R � þO2 ! RO2�

FILM DRYING PROCESS OF OIL-BASED COATING MATERIALS 315

and

RO2 � þRH! ROOHþ R�

The net reaction is hydroperoxide formation:

RHþ O2 ! ROOH

During the oxidation to form hydroperoxides, the natural cis,cis unsaturation of

linoleate is converted to cis, trans and trans, trans isomers. Privett and co-workers

(10) concluded that at least 90% of linoleate hydroperoxide preparations are conju-

gated. When the oxidation is conducted at 0�C the hydroperoxides are predomi-

nately cis, trans isomers, but room temperature oxidation produces a large

amount of trans, trans unsaturation (11, 12). Ethyl or methyl linoleate hydroperox-

ides are relatively low melting and as a result purification by crystallization is dif-

ficult. Bailey and Barlow (13) prepared high melting p-phenylphenacyl linoleate,

oxidized the ester in benzene solution, and isolated virtually pure hydroperoxide

by crystallization. Infrared spectra of the 99% purity p-phenylphenacyl linoleate

hydroperoxide correspond to a trans, trans conjugated isomer.

The autoxidation of linoleate described above shows the characteristic features

of a chain reaction involving free radicals. Materials that decompose to form free

radicals catalyze the reaction even when present in very low concentrations to

produce high yields of hydroperoxides; initiation of the reaction by light can pro-

duce quantum yields much greater than unity and easily oxidized substances that

consume free radicals, but do not themselves undergo significant autoxidation,

can markedly inhibit the chain reaction.

Although there is quite general agreement on the mechanism of the chain pro-

pagation reaction, there is much less unanimity of opinion on the primary reaction

to produce the radicals (indicated as A � above) responsible for the initiation of the

chain reaction. Originally, it was proposed that hydroperoxides are the initial pro-

ducts of autoxidation (14, 15). Primarily because of the high energy requirement for

rupture of the a-methylenic carbon–hydrogen bond several authors (16–19) almost

simultaneously concluded that the initial point of oxidative attack was the double

bond and not the a-methylene group, although some (16) proposed a limited attack

at the double bond to produce radicals in sufficient amount to initiate the chain reac-

tion through the a-methylenic carbon.

Kahn (20) questioned the formation of a diradical and proposed direct addition

of oxygen to a double bond to form a cyclic transition state, which breaks down

to yield the hydroperoxide. The theory of oxidation has received little support,

because it does not explain the inhibitory effect of free-radical acceptors in the ini-

tial stages of autoxidation.

It has been contended that the direct attack of oxygen on the double bond has

low thermodynamic probability (21, 22), and it has been considered that trace metal

contaminants catalyze the initiation of autoxidation by producing free radicals

through electron transfer. Alternative pathways are as follows, using cobalt as an


example of a metal that can facilely shift valence states in oxidation–reduction

reactions:

1. Reduction activation of trace hydroperoxides in the system yields free

radicals.

Co2þ þ ROOH! Co3þ þ OH� þ RO�

2. Direct reaction of a metal ion with oxygen:

Co2þ þ O2 ! Co3þ þ O�2 �

The O�2 � radical ion reacts readily with a proton to form the HO2� radical,

which can initiate the chain reaction of oxidation.

3. Complex reaction of metal compounds with oxygen and subsequent forma-

tion of an HO2� radical.

Co2þ þ O�2 ! Co3þ � O2

Co3þ � O2 þ XH! Co3þ þ X� þ HO2�

4. Oxidation by electron transfer of the a-methylenic group by the metal ion.

Co3þ þ RH! Co2þ þ Hþ þ R�

According to Uri (21) the kinetic and thermodynamic probabilities for formation of

free radicals by the metal-catalyzed initiation reaction are considerably more favor-

able than the Bolland and Gee (16) proposal of diradicals by direct oxidation of a

double bond.

Once hydroperoxides are formed, even in trace amounts, they can play a

profound role in the autocatalysis. Monomolecular decomposition yields two free

radicals:

ROOH RO HO+

A bimolecular reaction, perhaps proceeding through intermediate hydrogen bond-

ing, is more probable:

ROO H

HOOR [ROO H

HOOR] HOH RO RO2+ + +

Either the monomolecular or the dimolecular decomposition serves to feed new

radicals into the reaction to initiate the chain reaction of autoxidation. These radicals

may further react through different paths. They may follow a radical chain mechan-

ism or other well-known radical reactions, such as coupling or disproportionation.

FILM DRYING PROCESS OF OIL-BASED COATING MATERIALS 317

The reactions may lead to the formation of dimers or polymers or may achieve

cross-linking, resulting in an insoluble, infusible film (i.e., drying). Apparently,

the dominant reaction path depends on the temperature. At room temperature,

mostly C��O��C bonds are produced, whereas C��C bonds are predominantly

formed under baking conditions.

The free radicals may also undergo chain cleavage reactions. Low molecular

weight by-products, such as water, carbon dioxide, aldehydes, ketones, and alcohols

may be formed, which cause the odor and taste of the oils. The strong odor of

rancid soybean oil was shown to be caused by 2-pentylfuran found in oxidized oil

in storage (23).

Chemically, the air-drying of a nonconjugated oil such as linseed is character-

ized by the adsorption of 12–16% by weight of oxygen. The reactivity of drying

oils is based on the mesomeric stabilization of the radical intermediate: the un-

paired electron is delocalized over several carbon atoms, and less energy is required

to eliminate the proton as illustrated below (24).

3.2. Drying of a Conjugated System

Tung oil, whose dominant feature is the conjugated cis, trans, trans-9,11,13-octa-

decatrienoic acid, a-eleostearic acid, dries to a coherent film with absorption of

only 5% by weight of oxygen. Privett (25) suggested oxidation through 1,2- or

1,4-addition to the diene system to yield noncyclic peroxides. Faulkner (26) iden-

tified 1,6-peroxide in addition and suggested that the autoxidation does not proceed

via hydroperoxide groups but rather via cyclic peroxides. It has also been found that

the triene content decreased and the diene content increased in proportion to the

absorption of oxygen (27, 28). The main reaction is believed to consist of a direct

attack by oxygen on the C��C double bonds to form cyclic peroxides and dienes.

The peroxides then react with allylic methylene groups or thermally dissociate to

give radicals, initiating a radical chain reaction mechanism, forming polymers via

C��C or C��O��C bonds (29).

4. OLEORESINOUS VARNISHES

As noted, coating systems were advanced from oil-only vehicles to oleoresinous

varnishes for improved performances. These are basically oils that have been

Activation Energy Relative Rate

Triglycerides Mesomers (kJ/mol) of Oxidation

Stearate a 415 0

Oleate 2 335 1

Linoleate 5 289 120

Linolenate 11 168 330

aSaturated molecules.


‘‘hardened’’ or modified by treatment with one or more suitable resins, natural

or synthetic. The oils and resins are combined, usually by heating together

at temperatures of 250�C or above, until a homogeneous mixture is formed. In

most cases, it is simply a case of dissolving the resin or resins in the oil. In

some cases, chemical reaction may have taken place between the resin and the

oil, such as that between the methylol groups of a ‘‘heat-reactive’’ phenolic resin

and the double bonds of a drying oil in forming a chroman ring structure as shown

below (30):

OH

R

CH2OHHOH2C

+

R′CH

CH

R′′

O

C

CHCH

R

R′

H R′′HOH2C

Chroman ring structure

The major improvements obtained by incorporating resins into drying oils are faster

drying, greater film hardness, higher gloss, better water and chemical resistance,

and greater durability. The degree of property change depends on the type and

the amount of the resin incorporated in the oil. Varnish makers express the oil to

resin ratio in terms of oil length, which is defined as the number of gallons of oil

used per 100 lb of the resins in the varnish. Varnishes are categorized according to

their oil length as short- (5–15 gal), medium- (16–30 gal), and long-oil (30þ gal)

varnishes. These demarcations are somewhat arbitrary and not universally agreed.

From oleoresinous varnishes, the coatings industry progressed into alkyd resins.

While one might say that this was only an evolutionary change, it nevertheless did

open a new horizon for coating technologists and has been responsible for the long-

evity of oil-based coating materials. It behooves us to take a more comprehensive

look at the various aspects of alkyd resins.

5. ALKYD RESINS

Alkyd resins have been the workhorse for the coatings industry over the last half

century. The term alkyd was coined to define the reaction product of polyhydric

alcohols and polybasic acids, in other words, polyesters. However, its definition

has been narrowed to include only those polyesters containing monobasic acids,

usually long-chain fatty acids. Thus thermoplastic polyesters typified by polyethy-

lene terephthalate (PET) used in synthetic fibers, films, and plastics and unsaturated

polyesters typified by the condensation product of glycols and unsaturated dibasic

acids (which are widely used in conjunction with vinylic monomers in making

sheet molding compounds or other thermosetting molded plastics) are not consid-

ered as part of the alkyd family and are beyond the scope of the present discussion.

ALKYD RESINS 319

The first appearance of the term alkyd resin in the subject index of Chemical

Abstracts was in 1929, under ‘‘resins.’’ It was not until 1936 that alkyd resins was

listed in its alphabetical place, but still appeared as ‘‘see resinous products.’’ The

proliferation of literature on alkyd resins peaked in the 1940s through the 1960s.

Research activities on alkyds in the United States, as indicated by the number of

publications, has apparently tapered off in the last two decades. Readers who are

alkyd history buffs can find more detailed historical reviews (31–34).

In spite of the challenges from many new coating resins developed over the

decades, alkyd resins, as a family, have maintained a prominent position even until

today. There are two major reasons for such sustained popularity. First, alkyds are

extremely versatile. An alkyd technologist can choose from a large variety of reac-

tion ingredients and at widely different ratios to tailor the structure and properties

of the resin or to obtain similar resin properties from different ingredients, as their

availability or cost may sometimes so dictate. For almost any given coating appli-

cation, from baking enamels for appliances to flat house paints to clear wood

finishes, one can design an alkyd resin to meet the property requirements. The

second reason is that alkyd resins can be made at relatively low cost. Most of

the raw materials are fairly low cost commodity items, and major capital investment

and high processing cost are not needed to produce the resins.

5.1. Basic Reactions and Resin Structure

The main reactions involved in alkyd resin synthesis are polycondensation by ester-

ification and ester interchange. If one uses the following symbols to represent the

basic components of an alkyd resin: O R

O

O , a polyol molecule or radical;

X��A��X, a polybasic acid molecule or radical; and X��F, a mono-basic acid mole-

cule or radical, a schematic representation of the resin molecule can be given (Fig-

ure 1). As Figure 1 implies, there is usually some amount of residual acidity along

with free hydroxyl groups left in the resin molecules. The structure-property rela-

tionship and the principles commonly followed to design the resin structure will be

discussed below.

5.2. Classification of Alkyd Resins

Alkyd resins are usually referred to by a shorthand description based on a certain

way of classification or a combined classification, from which the general properties

Figure 1. Schematic representation of an alkyd resin molecule.


of the resin become immediately apparent. The commonly used bases for classi-

fication are as follows.

Drying versus Nondrying, and the Specific Source of Fatty Acids. Alkyd resins

can be broadly classified into the drying type and the nondrying type, depending on

the ability of their film to dry by air oxidation. This drying ability is derived from

the polyunsaturated fatty acids in the resin composition. If drying oils, such as

linseed oil, are the sources of the fatty acids for the alkyd, the resin would belong

to the drying type and is usually used as the film former of coatings or inks. On the

other hand, if the fatty acids come from nondrying oils, such as coconut oil, the

resin would be a nondrying alkyd. They are used either as plasticizers for other

film-formers, such as in nitrocellulose lacquers, or are cross-linked through their

hydroxyl functional groups to become part of the film former. More frequently,

an alkyd resin is classified by the source of the fatty acids, e.g., a linseed alkyd,

a tung oil-modified soy alkyd, and a coconut alkyd.

Classified by Oil Length or Fatty Acid Content. Probably inherited from oleo-

resinous varnish practice but with a different way of expression, alkyd resins are

also classified by their oil length. For an alkyd resin, the oil length is defined as

the weight percent of oil or triglyceride equivalent, or alternatively, as the weight

percent of fatty acids in the finished resin, for example, the resin represented in Fig-

ure 1. The structure indicates that the molar ratio of these three ingredients is

4 : 4 : 3. Assume that the polyol is glycerol, the polybasic acid is phthalic anhydride,

and the fatty acids came from soybean oil with an average molecular weight of 280.

The formula weight of the resin would be 1674 and the triglyceride equivalent of

the fatty acids would be 878, thus the oil length would be 52.4%. Alternatively, the

above resin would be described as one having 50.2% fatty acids. Since the over-

whelming majority of alkyd resins are based on phthalic anhydride, it is also

customary to describe an alkyd in terms of its phthalic anhydride content in per-

cents based on the finished resin.

By this approach, alkyd resins are classified into four classes:

It should be noted that these demarcations are arbitrary and may vary from author to

author. Furthermore, the boundaries are usually not clear-cut.

More frequently, alkyd resins are described by a combined classification in terms

of their oil length, the type of fatty acids, and any unusual ingredients. Such

descriptions as an isophthalic, very long tall oil alkyd or a medium oil dehydrated

castor-PE (the PE refers to pentaerythritol, not polyethylene) alkyd or a short oil

lauric-benzoic alkyd would immediately project the general properties of the resin.

Percent Fatty Percent Phthalic

Resin Class Percent Oil Acids Anhydride

Very long oil >70 >68 <20

Long oil 56–70 53–68 20–30

Medium oil 46–55 43–52 30–35

Short oil <45 <42 >35

ALKYD RESINS 321

5.3. Oil Length–Resin Property Relationship

Obviously, the oil length of an alkyd resin has profound effects on the properties of

the resin. A few of these effects are discussed below.

Effect on Solubility. At long oil lengths, the aliphatic hydrocarbon chains of the

fatty acids constitute the major portion of the mass of the resin molecules; there-

fore, the resin would be soluble in nonpolar aliphatic solvents. Conversely, as the

oil length decreases and the phthalic content increases, the aromaticity of the resin

molecules increases, and the aromaticity and/or the polarity of the solvent will also

need to be increased to dissolve the resin effectively.

Effect on Drying Characteristics. Alkyd resin molecules have a comblike struc-

ture, with a thermoplastic polyester backbone and dangling fatty acid side chains.

Each of these two fractions contributes to the drying, or film-forming, characteris-

tics of the resin. The backbone fraction dries by solvent release, similar to a lacquer

material, whereas the side chain fraction dries in a manner similar to the oil from

which the fatty acids came. Therefore, short oil alkyds develop a surface dryness

relatively quickly due to a faster solvent release, which is often further facilitated

by the fact that the solvents used have high volatility. However, their through-dry in

air is usually slower, because the fatty acid side chains are fewer in numbers and

more scattered in space to cross-link with each other through the action of oxygen,

and the dry surface would impede the transportation of air oxygen to reach down

into the film. On the other hand, long oil alkyds are relatively slow in reaching the

‘‘set-to-touch’’ stage of surface drying, but the greater abundance of fatty acid side

chains and the relative openness of the film surface would facilitate the film to reach

through-dry.

Other trends of changing properties (Table 1) would become obvious, consi-

dering how the structure of resin molecules would change with oil length. Theoreti-

cally, one could design and make alkyd resins at almost any oil length. However, for

any given set of starting ingredients, as the oil length goes up, it will reach a point

TABLE 1 Trends of Property Changes with Oil Length of Alkyd

Resinsa.

Oil Length Long Medium Short

Requirement of aromatic, polar solvents ��!Compatibility with other film formers ��!Viscosity ��!Ease of brushing ��Air dry time, set-to-touch, ��Through-dry �� !Film hardness ��!Gloss ��!Gloss retention ��!Color retention ��!Exterior durability �� !aPrimarily referring to drying-type alkyds.


where the maximum extent of fatty acid modification of the polyester molecules has

been achieved, and any additional amounts of fatty acids or oil remain as separate

entities, blended with the polyester molecules. Refer again to the resin structure in

Figure 1. If the molar ratio is 1 : 1 : 1 among glycerol, phthalic anhydride, and soy

acids and the reaction was carried to completion, the resin would have an oil length

of 60.5%, or 57.9% of fatty acids. There is no more room in the resin structure to

accommodate any additional amount of fatty acid. Therefore, with those three

ingredients, if the oil length exceeds 60.5%, the excess amount of oil would only

be retained in the resin as a blend. Obviously, the ‘‘very long oil’’ types of alkyd

resins would almost certainly be resin–oil blends.

The maximum oil length of an alkyd resin (before it becomes a resin–oil blend)

depends on the molecular weight of the ingredients as well as the functionality of

the polyol. If the C18 soy fatty acids in the above example is replaced with C12

lauric acid, the transition would be reached at 52.6% oil. On the other hand, if a

tetra-hydroxyl polyol, such as pentaerythritol, replaces glycerol, the stoichiometry

would allow 2 moles of fatty acids, for every 1 mole of phthalic anhydride and

pentaerythritol. Thus theoretically, the maximum amount of soy fatty acids that

may be chemically combined in the resin structure would be 70.9%, equivalent

to a 74.1% oil length.

5.4. Major Ingredients

Each of the three principal components of alkyd resins—the polybasic acids, the

polyols, and the monobasic acids—has a large variety to be chosen from. The selec-

tion of each one of these ingredients will affect the properties of the resin. As will

be shown later, the choice of ingredients may even affect the choice of manufac-

turing processes. To both the resin manufacturers and the users, the selection of the

proper ingredients is a major decision.

Polybasic Acids and Anhydrides. The major types of polybasic acids used in

alkyd preparation are as follows.

Phthalic anhydride is by far the most important dibasic acid used in alkyd prepara-

tion, because of its low cost and the excellent overall properties it imparts to the

Molecular Equivalent

Type Weight Weight

Phthalic anhydride 148 74

Isophthalic acid 166 83

Maleic anhydride 98 49

Fumaric acid 116 58

Adipic acid 146 73

Azelaic acid 160 80

Sebacic acid 174 87

Chlorendic anhydride 371 185.5

Trimellitic anhydride 192 64

ALKYD RESINS 323

resin. Its anhydride structure allows a fast esterification to form half-esters at rela-

tively low reaction temperatures without liberating water, thereby avoiding the dan-

ger of excessive foaming in the reactor. However, since the two carboxyl groups of

phthalic anhydride are in the ortho position to each other on the benzene ring,

cyclic structure may and does occur in the resin molecules. Consequently, the

development of chain length of the polymer would be restricted, and the average

molecular weight would tend to be low. Phthalic anhydride has a tendency to sub-

lime. (Heat of sublimation: 143 g-cal/g; heat of vaporization: 87.2 g-cal/g.) There-

fore, care must be taken to prevent its loss.

Isophthalic acid is the meta isomer of phthalic acid. Since the two carboxyl

groups are adequately separated, the chances of forming a cyclic structure in the

resin molecules are greatly diminished. Therefore, isophthalic alkyds usually attain

higher molecular weight and show much higher viscosity than their phthalic coun-

terparts at the same oil length. This is the major motivation for resin manufacturers

to use isophthalic acid for the preparation of long oil alkyds. Another major

advantage of isophthalic acid is that the resultant alkyd resins show much higher

thermal stability than the phthalic type (35). In spite of these advantages, isophtha-

lic acid has not gained the same popularity as phthalic anhydride in alkyds, because

the resin making process is much more complicated and difficult than that with

phthalic anhydride. Its melting point (350�C) is much higher than that of phthalic

anhydride (131�C), and it has a low solubility in the initial alkyd reactants, which

causes the reactants to stay as a two-phase solid–liquid system and does not become

clear until the reaction is near complete (36, 37). The diacid does not readily form

half-esters at relatively low reaction temperature as would the anhydride, and twice

as much water will be formed and needs to be removed from esterification. Usually,

additional care and equipment are needed for the higher processing temperature

required for isophthalic acid.

The para isomer terephthalic acid may also be used for making alkyds. The

resultant resins showed even better thermal stability than isophthalic alkyds (35).

However, it has all the disadvantages of isophthalic acid and is more expensive.

It is rarely used in making alkyd resins.

Maleic anhydride is sometimes used for partial substitution of phthalic anhy-

dride in making alkyds. It imparts vinylic unsaturation functionalities in the back-

bone chain of the resin molecules, which allows the resin to be grafted with styrene,

acrylic esters, or other vinyl monomers. The presence of a small amount of maleic

anhydride, up to 10% on molar base of the total dibasic acids, in the resin formula-

tion would accelerate the viscosity increase during the resin manufacturing process.

The resins usually dry more rapidly and give harder films with improved color,

adhesion, water resistance, alkali resistance, and exterior durability. However, the

resin cooking process needs to be monitored and controlled with greater care, parti-

cularly when it is near the desired end point, to prevent gelation. Fumaric acid, the

trans isomer of maleic acid, may be used in an equivalent manner.

Maleic and fumaric acid can also be, and are often, incorporated in alkyd resins

in the form of the Diels-Alder adduct of rosin. The adducts are tribasic acids. They

provide one of the means to impart pendant carboxyl groups in the resin molecules,


which can then be saponified to give ionic and, in turn, water-soluble characteristics

to the resin. Alkyds containing maleic–rosin adducts often have poorer color reten-

tion, toughness, gloss retention, and exterior durability.

Aliphatic dibasic acids, such as succinic, adipic, azelaic, and sebacic acids have

also been used to make alkyd resins. Their linear and flexible chain structure lends

higher flexibility and lower viscosity to the resin than the rigid aromatic rings of

phthalic acids.

Chlorendic anhydride is the Diels-Alder adduct of maleic anhydride and hexa-

chlorocyclopentadiene. It is also known as hexachloro-endo-tetrahydrophthalic

(HET) anhydride. The major interest of the alkyd industry in this material is that

the resultant resins contribute to the flame retardancy of the coatings. It has been

reported to give a greater reaction rate than phthalic anhydride, such that at 204–

210�C (400–410�F) the reaction rate approximates that of phthalic anhydride at a

temperature of 238�C (460�F) (38). However, the resins are prone to develop darker

color, particularly at high processing temperature. Tetrachlorophthalic anhydride,

made by conventional chlorination of phthalic anhydride, would also impart flame

retardancy to its alkyds. However, it is appreciably less soluble in the usual proces-

sing solvents than is phthalic anhydride and is reported to be of appreciably lower

chemical reactivity (39).

Trimellitic anhydride (TMA), 1,2,4-benzenetricarboxylic acid anhydride, has

gained greater prominence in recent years due to the greater interest in water-

soluble alkyds. A partial substitution of the phthalic anhydride with TMA gives a

measured quantity of pendent carboxyl groups for water solubilization with

ammonia or other suitable base. The anhydride hydrolyzes to the acid form simply

by allowing it to stand in open containers. Premature cross-linking of alkyd resins

formulated with a high content of TMA would occur at high acid numbers when

large amounts of trimellitic acid are present (40).

Polyhydric Alcohols. The major types of polyol used in alkyd synthesis are as

follows.

Pentaerythritol (PE) is one of the most important polyols used in alkyd resins. Its

molecular structure, four methylol groups (CH2OH) surrounding a center carbon

atom, is the basis for its many interesting attributes. The four equal and highly

Molecular Equivalent

Type Weight Weight

Pentaerythritol 136 34

Glycerol 92 31a

Trimethylolpropane 134 44.7

Trimethylolethane 120 40

Ethylene glycol 62 31

Neopentyl glycol 104 52

aSince glycerol is usually supplied at 99% purity (1%

moisture), its equivalent weight is commonly assumed to

be 31 in recipe calculations.

ALKYD RESINS 325

reactive primary hydroxyl groups make it versatile for designing resin structures,

and the neopentyl core structure lends stability against heat, light, and moisture.

As a result, alkyds based on PE usually are superior to their counterparts based

on glycerol in viscosity, drying properties, film hardness, gloss retention, color

and color stability, humidity resistance, thermal stability, and exterior durability.

On the other hand, its high functionality demands that the resin composition be

more carefully designed and the synthesizing process be more carefully monitored

and controlled to reduce or eliminate the tendency of gelation. Dipentaerythritol

and tripentaerythritol are linear dimer and trimer of PE. They are hexa- and octa-

functional polyols, respectively. Technical grades of PE usually contain small or

trace quantities of di- and tri-PE that were not completely removed in the manufac-

turing process. The high functionality of these materials makes them impractical to

be considered as the sole or major polyol of an alkyd resin.

Among the triols, glycerol is undoubtedly the most important one in alkyd tech-

nology. Natural fats and oils are triglycerides. Therefore, whenever oils are used

directly as the source of fatty acids in an alkyd resin, glycerol will automatically

be a part of the polyols of the resin. Besides the difference in functionality, the

major difference between glycerol and PE is that one of the hydroxyl groups in

glycerol is secondary, which has lower reactivity than primary hydroxyl groups.

This often manifests itself as if glycerol had a de facto functionality of less than

3. Consequently, a larger excess of glycerol would be required in the resin formulas,

which would result in poorer resin properties as a coating material. At high tempe-

ratures, the proton on the secondary carbon in glycerol may undergo a dehydration

reaction with one of the primary hydroxyl groups on the adjacent carbon atom to

give water and acrolein, whereas such reaction is not possible with PE. Glycerol

alkyds are more prone to thermally decompose to give color bodies, resulting in

darkening of the resin.

Trimethylolethane and trimethylolpropane are synthetic triols. Like PE, they

have the neopentyl structure and equivalent primary hydroxyl functional groups.

Therefore, they also yield alkyds with better resistance to heat, light, moisture, and

alkali than glycerol. They have one less hydroxyl group than PE, and the equivalent

weights of these polyols are higher than that of PE. Trimethylolethane has been

reported to give alkyds that are faster drying and higher in film hardness than tri-

methylolpropane (41), whereas trimethylolpropane was claimed to give alkyds with

better water and alkaline resistance, color and color retention, and impact resistance

than trimethylolethane (42).

Diols such as ethylene glycol, propylene glycol, and neopentyl glycol are some-

times used as part of the polyols in alkyd formulations primarily for the purpose of

regulating the functionality of the reaction system. Their relatively low boiling

points, (197, 188, and 207�C), respectively, for the above three glycols) require that

special precautionary measures be taken during the resin manufacturing process.

Analogous to the use of linear a,o-dibasic acids (such as adipic and sebacic),

polyols with long, flexible chains between hydroxyl groups (such as 1,4-butanediol,

1,6-hexanediol, and diethylene glycol) may also be used to impart greater flexibility

in the resin.


It should be pointed out that under high temperatures, such as those used for

alkyd resin synthesis, and in the presence of high acidity, etherification between

the hydroxyl groups of two polyol molecules may condense them into a new polyol

with a functionality of nþ n0 � 2, where n and n0 are the numbers of hydroxyl

groups of the two original molecules. The introduction of such high functionality

polyols plus the net reduction of total available hydroxyl groups can lead to an

increased danger of gelation during the poly-condensation process.

Monobasic Acids. The overwhelming majority of monobasic acids used in alkyd

resins are long-chain fatty acids of natural occurrence. They may be used in the

form of oil or free fatty acids. Free fatty acids are usually available and classified

by their origin, viz., soy fatty acids, linseed fatty acids, coconut fatty acids, etc. The

fatty acid composition of various types of fats and oils that are commonly used in

alkyd resins are given in Table 2.

The drying property of alkyd resins reflects directly that of the oil or fatty acids

in the resin structure, discussed earlier. It should be pointed out that alkyds based on

conjugated unsaturated fatty acids, such as those from tung and oiticica oils, dry so

fast that if not properly moderated, the surface layer will dry long before the under-

layer, resulting in a wrinkled surface due to the stresses created in the dried surface

layer. Therefore, in alkyd resins, tung oil and oiticica oil are primarily used to fur-

nish a minor portion of the fatty acids to improve drying properties. Even so, great-

er care must be exercised during the manufacturing process to avoid gelation, which

is caused by the dimerization of the fatty acid chains through a Diels-Alder addition

between the conjugated diene structure on one molecule and a double bond on

another molecule. It should be noted that nonconjugated diene groups, such as those

in linoleic and linolenic acids, may undergo isomerization to become conjugated.

Furthermore, ene-reaction could also occur between two unsaturated fatty acid

chains, which leads to gelation.

Rheineck and co-workers (44) have found that linolenic acid is responsible for

the high yellowing tendency of alkyds based on linseed oil fatty acids. Therefore,

alkyds intended for making white or light color enamels should avoid high linolenic

content fatty acids by choosing soy oil, safflower oil, or dehydrated castor oil

(DCO). Alkyds made with nondrying oils or their fatty acids have excellent color

and gloss stability. They are frequently the choice for white industrial baking enam-

els and lacquers.

Since the mid-1950s, tall oil fatty acids (TOFA) have become available in good

quality and large quantities. Refined grades of TOFA have degrees of unsaturation

rivaling that of soy acids. Since it is a year-round by-product from the paper indus-

try, its supply and price are more stable than agricultural products like soy fatty

acids. It is used extensively in medium- to long-oil alkyds, virtually as equivalent

to soy fatty acids. Although the minor quantities of rosin acids in TOFA may impart

some yellowing tendency, its lack of linolenic acid may be more than enough to

give as good or even better color retention than soy fatty acids. The typical proper-

ties of refined grades of commercial TOFA are given in Table 3.

A number of monobasic acids that are not derived from fats and oils have been

used in alkyd resins. However, except in the rare cases of making the so-called

ALKYD RESINS 327

TABLE 2. Fatty Acid Compositions of Fats and Oils Commonly Used in Alkyd Resins.

Fatty Acid Composition (Percent by Weight)

Oil Iodine Value Saponification Value Saturateda Palmitoleic Oleic Linoleic Linolenic Other

Castor 85.8 195 2.4 — 7.4 3.1 — Ricinoleic, 87.0; dihydroxystearic, 0.6

Castor, 125–135 191 2.4 — 8.0 86 3.0 About 33% of the linoleic is

dehydrated 9,11-conjugated.

Coconut 8.7 257 76.6 — 5.7 2.6 — Caprylic, 7.9; capric, 7.2; of the

saturated, lauric, 48.0 and

myristic, 17.5

Cottonseed 105.0 196 27.2 2.0 22.9 47.8 — Tetradecenoic, 0.1

Linseed 180 191 9.3 — 19.0 24.1 47.4 Lignoceric, 0.2

Menhaden 148–185 191 24.0 15.0 30.0 — — Highly unsaturated

C20H2(20� x)O2, 19; and

C22H2(22� x)O2, 12.b

Oiticica 192 11.3 — 6.2 — — Licanic, 82.5

Peanut 93.3 190 13.8 1.7 54.3 26.0 — Arachidic, 2.4; behenic 3.1:

lignoceric, 1.1

Rapeseed 102.3 175 6.1 1.5 12.3 15.8 8.7 Behenic, 0.7: lignoceric, 0.8;

eicosenole, 4.8; erucle, 47.8;

docosendienole, 1.5

Safflower 136.2 191 6.0 — 32.8 61.1 1

Soybean 132.6 193 13.4 1.0 23.5 51.2 8.5 Saturated C20-C24, 2.4

Sunflower 130.8 188 7.1 — 34.0 57.5 — Lignoceric, 0.4

Tung 192 5.0 — 5.0 3.0 — Eleostearic, 87

aAliphatic monocarboxylic acids, C12 to C20, principally palmitic and stearic.bx ¼ 4� 10.

Owing to incomplete halogen absorption, iodine values for conjugated acid oils by the usual methods (Wijs, Hanus, etc.) are both low and variable. The true value of fresh tung

oil, as determined by special method, is 248–252: that of oiticica oil is 205–220 (43).

oil-free alkyds for special purposes, they are used in conjunction with fatty acids to

modify resin properties. Rosin acids, primarily in the form of abietic acid, are the

most common type of such acids. They may be used in neat form or be brought in

as a part of TOFA. Presumably, the fused ring structure of rosin contributes to the

film hardness, initial gloss, and water resistance of the alkyd. However, color and

color retention, and exterior durability will be adversely affected if the rosin content

goes much above 5–6%. The drying rate of alkyds usually appears to be improved

with rosin modification. However, since rosin does not participate in the oxidative

drying mechanism that applies to polyunsaturated fatty acids, the true drying rate of

the alkyd resin would be reduced due to a reduction of the fatty acid unsaturation.

Synthetic saturated carboxylic acids (such as pelargonic acid, 2-ethylhexanoic acid,

and isoctanoic acid) and aromatic monobasic acids (such as benzoic acid and

p-alkyl-benzoic acids) can improve color retention, gloss retention, and exterior

durability even better than those based on castor or coconut fatty acids. The aro-

matic acids, similar to rosin, also give higher film hardness and faster apparent

drying rate.

5.5. The Concept of Functionality and Gelation

The concept of functionality and its relationship to polymer formation was first

advanced by Carothers (45) in 1929. Flory (46) greatly expanded the theoretical

consideration and mathematical treatment of polycondensation systems. Thus if a

dibasic acid and a diol are reacted to form a polyester, assuming there is no possi-

bility of other side reactions to complicate the issue, only linear polymer molecules

TABLE 3. Typical Properties of Refined Tall Oil Fatty Acidsa.

Grade Designation

Pamak Pamak Pamak Pamak Pamolyn Pamolyn

Characteristic 1 2 4A 4 200b 300a

Acid number 193 192 191 188 195 196

Iodine number 125 128 130 131 162 156

Total fatty acids, % 96.8 95.9 94.1 91.5 97 97

Saturated acids, % of free fatty acids 2.0 — — 4.0 <1 <1

Oleic 51.0 — — 51.0 22.0 21.0

Linoleic, nonconjugated 41.0 — — 39.0 68.0 39.0

Linoleic, conjugated 6.0 — — 6.0 10.0 40.0

Linolenic — — — — — —

Rosin acids, % 1.4 1.8 3.5 4.0 1.5 1.5

Unsaponifiables, % 1.8 2.3 2.4 4.5 1.5 1.5

Color, Gardner 3 3 4 6 3þ 3

Titer, �C 5 5 5 6 �28 �28

aData from Hercules, Inc. (Wilmington, Del.).bEnriched polyunsaturated fatty acids from highly refined TOFA.cSame as Pamolyn 200, with further treatment to isomerize the nonconjugated linoleic acid.

ALKYD RESINS 329

will be formed. When the reactants are present in stoichiometric amounts, the aver-

age degree of polymerization �xxn follows the equation:

�xxn ¼ 1=ð1� pÞ ð1Þ

where p is the extent of reaction, in fractions. Thus when the reaction is driven to

completion, theoretically, the molecular weight would approach infinity and the

whole mass would form one giant polymer molecule. Although the material should

theoretically be still soluble and fusible, it is considered and defined as a gel, and

this would be the only time that difunctional ‘‘monomers’’ could be polymerized to

gelation.

The functionality of the system f is the sum of all of the functional groups, i.e.,

equivalents, divided by the total number of moles of the reactants present in the

system. Thus in the above equimolar reaction system:

f ¼ ð1� 2þ 1� 2Þ=ð1þ 1Þ ¼ 2

However, when there are reactants with three or more functionalities participating

in the polymerization, branching and the formation of intermolecular linkages (i.e.,

cross-linking of the polymer chains) become definite possibilities. If extensive

cross-linking occurs in a polymer system to form network structures, the mobility

of the polymer chains is greatly restricted. Then the system would lose its fluidity

and transform from a moderately viscous liquid to a gelled material with infinite

viscosity. The experimental results of several such reaction systems reported by dif-

ferent investigators are collected in Table 4.

The data in Table 4 show that when the reactants are present in stoichiometric

proportions, gelation occurs before the completion of esterification, and the extent

of reaction p reached at the gel point depends on the functionality of the system.

Carothers (47) showed that at the gel point, p ¼ 2=f . Thus, to avoid premature

gelation, the polymerization system should have an average functionality of no

more than 2. This can be accomplished by adding low functionality reactants

and/or adding an excess amount of one of the reactants, usually the one with high

functionality constituents. The latter has the net effect of reducing the functionality

of the reactant. For example, if a 20% excess of glycerol over the stoichiometric

TABLE 4. Gel Points of Polyesterification Reaction Systems with Stoichiometric

Reactants (46).

Percent Esterification

Polybasic Acid (COOH) Polyol (OH) f at Gel Point

Adipic (0.707)þ tricarballylic (0.293) di-EG (1.0)a 2.103 0.911

Dibasic (1.0) glycerol (1.0) 2.400 0.765

Adipic (1.0) PE (1.0)b 2.667 0.578

aDiethylene glycol.bPentaerythritol.


amount required to esterify all of the carboxyl groups present in the formula is

added, the glycerol would have an effective functionality of 3/1.2, or 2.5. Fre-

quently, both of these measures are taken to safeguard against premature gelation.

Patton (48) showed that for alkyd resins, the extent of the reaction at gel point was

pc ¼ 2=f ¼ 2mo=eo

where eo is the total effective equivalents of all of the reactants present at the begin-

ning of the reaction (i.e., the excess reactants are discounted in the manner dis-

cussed above), mo is the total number of moles of all reactants at the beginning,

and f is the effective average functionality of the formulation.

5.6. Microgel Formation and Molecular Weight Distribution

Bobalek and co-workers (49) observed that the behavior of alkyd resin reaction

often deviates from that predicted by the theory of Flory. They proposed a mecha-

nism of microgel formation by some of the alkyd molecules at a relatively early

stage of the reaction. The microgel particles would be dispersed and stabilized

by smaller molecules in the remaining reaction mixture. As polyesterification pro-

ceeds, more microgel particles would be formed, until finally a point is reached at

which they could no longer be kept separated. The microgel particles would then

coalesce or flocculate, phase inversion would occur, and the entire reaction mass

would be ‘‘gelled.’’ They showed that the drying capability of an alkyd resin comes

primarily from the microgel fraction and, ‘‘when the highest molecular weight frac-

tion representing about 20% of the total was removed through fractionation, the

residual linoleic alkyd lost all ability to air dry to a hard film.’’

Solomon and co-workers (50, 51) further elaborated on the microgel theory by

proposing the formation of micelles as precursors of microgels. They proposed that

when some of the molecules have grown to reach certain fatty acid: polyester ratios,

surface activity develops to form micelles. The polyesterification reactivity at the

surface of the micelles would be preferentially greater, which would lead to the

eventual formation of microgels. From electronmicroscopy evidence, they observed

that the size of microgels increased with reaction time, and particle diameters as large

as 2m have been reported. Functional groups such as OH groups in the microgel

particles are believed to be buried in the structure and not available for reactions.

Whereas in polyesterification reactions without fatty acids, at all stages of the reac-

tion up until the physical gelation of the reaction mixture, the hydroxyl values cor-

responded with the calculated values. Furthermore, the oil-free systems showed no

sign of microgel formation under electron microscope, and the reaction mixture

would undergo a sudden change from a soluble polymer to a gelled mass. The reac-

tion temperature for alkyd preparation in both of the above references was kept at

no more than 200�C, well short of what would normally be required for the bodying

of unsaturated oils in the absence of an oxidizing reagent. This indicates that poly-

merization between unsaturated fatty acids of the resin molecules is not necessary

for the formation of microgels.

ALKYD RESINS 331

Kumanotani and co-workers (52–55) further confirmed the formation of micro-

gels by characterizing fractions of alkyd resins from preparative GPC columns.

Their results showed that the presence of microgel can be detected even in low

molecular weight fractions. Colloidal gel particles up to 10þ mm in diameter

were observed in the high molecular weight (>105) fractions, with or without unsa-

turated fatty acids in the alkyd formulation. However, the unsaturated fatty acids

made a significant contribution to the formation of the colloidal particles. Higher

reaction temperature led to higher molecular weight and broader molecular weight

distribution. Acid value and hydroxyl value each went through a minimum in the

middle fractions (molecular weight about 103–104), whereas the polyester: mono-

acid ratio increased with the molecular weight of the fraction. Cured films from

alkyds with greater amount of colloidal fractions gave better thermomechanical

properties. Finally, the high molecular weight colloidal fractions were preferentially

adsorbed by pigment particles and would thus stabilize the pigment dispersion in

the coating formulation.

5.7. Basic Principles for the Designing of Alkyd Resins

The process of alkyd resin designing should begin with the following question:

what would be the intended application(s) of the resin? The application would

dictate property requirements, such as solubility, viscosity, drying characteristics,

compatibility, film hardness, film flexibility, acid value, water resistance, chemical

resistance, environmental endurance, etc. With these targets in mind, a selection on

oil length, and a preliminary list of alternative choices of ingredients can then be

made. For commercial production, the raw material list is screened based on consi-

derations in material cost, availability, yield, impact on processing cost, and poten-

tial hazard to health, safety, and the environment. The list may be further narrowed

by limitations imposed by the production equipment or other considerations. Once

the oil length and ingredients are chosen, the first draft of a detail formulation for the

resin can then be made.

It would be highly desirable that one could rely on a simple equation or formula

to obtain the optimum formulation of the alkyd resin with the chosen ingredients,

and several approaches have been proposed for such purpose (56–59). However, the

complexity of the alkyd reaction system has rendered these equations to be of no

more value than providing a first approximation of a starting formula. The causes of

the complexities include the formation of intramolecular cyclic structures, which

would reduce the chance of gelation; the etherification of polyols, which would

increase the chance of gelation by forming higher functionality materials and redu-

cing the number of hydroxyl groups available for esterification; the cross-linking

between unsaturation groups, especially the conjugated double bonds, which would

increase the chance of gelation; and the phenomenon of microgel formation.

Except when nondrying alkyds are used strictly as plasticizers for other thermo-

plastic polymers, alkyd resins do not remain as a thermoplastic material in their

ultimate application. The film integrity is largely derived after the resin molecules

have been cross-linked, either through the unsaturation functionalities on their fatty


acid side chains or through the reactions of their residual hydroxyl or carboxyl

functionalities with such cross-linking agents as amino resins or polyisocyanate

materials. In a sense, alkyds are usually made and applied as B-stage resins. There-

fore, it is not necessary to build the molecules of alkyd resins to huge molecular

weights, as one would for thermoplastic polymers. In fact, too high a molecular

weight would lead to poor solubility and high solution viscosity and would be un-

desirable for practical applications. Most of the published data show that the aver-

age molecular weight of alkyds is less than 10,000. Nevertheless, within the

practical limits, it is still preferred to have a linear backbone structure and high

molecular weight to give the best film-forming and film properties. Alkyd formula-

tions with an equimolar ratio of dibasic acids: polyols tend to have the best chance

of achieving a linear molecular structure and high molecular weight.

Thus a simple molecular approach is favored by some of the alkyd chemists for

deriving the starting formulation. The basic premise of this approach is that when

the total number of moles of polyols is equal to or slightly larger than that of the

dibasic acids and the hydroxyl groups are present in an empirically prescribed

excess amount, the probability for gelation to occur would be small. Table 5 lists

the empirical requirements of excess hydroxyl groups based on the oil (fatty acid)

length of the alkyd. The values were developed based on experimental experience

(57, 58). With the new understanding that some of the hydroxyl groups would be

buried in microgel structures (49–55), such requirements may be better rationa-

lized. The procedure of this method for formulating alkyd resins will be illustrated

with examples.

The first example demonstrates the formulations of a 50% soy oil alkyd for

baking enamels. The preliminary selection of ingredients would be alkaline refined

soy oil, phthalic anhydride (PA), and pentaerythritol. The basis for calculation is

1 mole of PA. From Table 5, the excess OH recommended at 50% oil length

is 25%. Therefore, the quantity of PE required, in equivalents, would be

EPE ¼ 1� 2� ð1þ 0:25Þ ¼ 2:5 eq: ¼ 0:625 moles

TABLE 5. Excess Hydroxyl Content Required in Alkyd Formulations.

Oil Length, Percent Percent Excess OH Based Percent Excess OH

Fatty Acida on Diacid Equivalents in Finished Resin

62 or more 0 0

59–62 5 0–5

57–59 10 5–10

53–57 18 10–15

48–53 25 15–20

38–48 30 20–25

29–38 32 25–30

aBased on C18 fatty acids with average equivalent weight of 280. If the average

equivalent weight of the monobasic acids is significantly different, adjust

accordingly.

ALKYD RESINS 333

Since the total polyol is to be equimolar to PA, the glycerol from the soy oil will,

therefore, be ð1� 0:625Þ ¼ 0:375 moles, which gives ð3� 0:375Þ ¼ 1:125 moles

of soy fatty acids. The ingredients can be listed as follows:

The above formulation does not meet the test of 50% oil length. The oil content

must reduced. A reduction in oil would cause a corresponding reduction in glycerol,

consequently, free glycerol is added to make up the loss. Let MPE ¼ X, MGly ¼ Y ,

and Moil ¼ Z. Since the total polyols is to be equimolar to dibasic acids, X þ YþZ ¼ 1. The 25% excess OH requirement defines 4X þ 3Y ¼ ð2� 1:25Þ ¼ 2:5, and

the 50% oil length requirement gives the following:

880Z=ð148þ 141:6X þ 93Y þ 880Z � 18Þ ¼ 0:5

where 880, 148, 141.6, 93, and 18 are the molecular weights of the oil, PA, PE,

glycerol, and water, respectively. When solve the simultaneous equations to find

X ¼ 0:221, Y ¼ 0:539, and Z ¼ 0:240. Thus the ‘‘final’’ formulation is listed as

follows:

The above formulation meets all of the requirements of the resin design, i.e., equi-

molar PA and polyols, 25% excess OH, and 50% oil.

The next example shows the formulation of a 50% TOFA alkyd for baking

enamels. Assume that PA, PE, ethylene glycol (EG), and refined TOFA with

4% rosin acids are the chosen ingredients. From the given constraints, the

Ingredient M COOH OH Weight (g)

PA 1.0 2.000 — 148.0

Soy oil 0.240 0.720 0.720 211.2

Glycerol 0.539 — 1.617 50.1

Tech-PE 0.221 — 0.884 31.3

Total 2.000 2.720 3.221 440.6

Water 1.0 — — (18.0)

Resin — — — 422.6


PA 1.0 2.000 148.0

Soy oil 0.375 1.125 1.125 330.0

Tech-PE 0.625 — 2.500 88.5

Total 2.000 3.125 3.625 566.6

Water 1.0 — — (18.0)

Resin — — — 548.5


following simultaneous equations can be established. Let MEG ¼ X, MPE ¼ Y , and

MTOFA ¼ Z.

X þ Y ¼ 1

2X þ 4Y ¼ 2� ð1þ 0:25Þ þ Z

295Z � ½148þ 141:8Y þ 62X þ 295Z � 18� ð1þ ZÞ� ¼ 0:5

Solve the equations, to find X ¼ 0:362, Y ¼ 0:638, and Z ¼ 0:776. Therefore, the

‘‘final’’ formulation can be listed as follows:

The percent excess OH ¼ ð3:276� 2:776Þ=2 ¼ 25%, and the oil length ¼228:9=457:6 ¼ 50% TOFA.

The ‘‘final’’ formulations derived in the above examples are meant to be only the

starting formulations. They should be fine-tuned based on small-scale laboratory

experiments before being used in plant production.

Since the molecular chain length or the degree of polymerization is a function of

the extent of the reaction as shown in equation 1, the alkyd reaction is usually car-

ried to a point short of completion, i.e., to a finite acid number to guard against

premature gelation. It has been shown that the esterification of phthalic anhydride

was slower and showed higher temperature dependence, i.e., higher activation

energy, than that of fatty acids (60–62). Therefore, one may assume that the residual

acidity belongs to unreacted dibasic acids, which contributes to the limiting of

chain growth. In real practice, an additional safety margin against premature

gelation is provided by having a slight molar excess of polyols over dibasic acids

in the alkyd formulation. If the molar ratio between the polyols and the dibasic

acids is r, equation (1) may be rewritten as:

�xxn ¼ ð1þ 1=rÞ=½ð2=rÞð1� pÞ þ 1� 1=r� ð2Þ

which indicates that a fractional increment in r and/or a fractional reduction in p

would give a substantial reduction in �xxn. Generally, the value of r is chosen between

1 and 1.05.


PA 1.000 2.000 — 148.0

Tech-PE 0.638 — 2.552 90.3

EG 0.362 — 0.724 22.4

TOFA-4 0.776 0.776 — 228.9

Total 2.776 2.776 3.276 489.6

Water 1.776 — — (32.0)

Resin — — — 457.6

ALKYD RESINS 335

5.8. Chemical Procedures for Alkyd Resin Synthesis

Different chemical procedures may be used for the synthesis of alkyd resins. The

choice is usually dictated by the choice of the starting ingredients.

Alcoholysis Process. Cost and availability often dictate that oil, rather than free

fatty acids, be used as raw material for alkyd synthesis. Since oil, in the form of

triglycerides, is essentially inert and would not participate in the polyesterification

reaction, heating the oil with the polyol and the dibasic acid would result in the

formation of seedy polycondensates between the polyol and the polybasic acids

leaving the oil unreacted. The two phases thus would be incompatible with each

other. Therefore, the triglycerides must first react with additional polyol to redistri-

bute the fatty acids among all of the polyols, thereby liberating free hydroxyl groups

from the oil for further reaction with the dibasic acids. The reaction is alcoholysis.

It is usually catalyzed by basic compounds such as metal oxides, hydroxides, salts,

or soaps such as naphthanates. In the past, litharge was the most popular choice as

the catalyst. It was found that on a molar basis lead compounds were the most effi-

cient among the 36 that were included in the study (58). In recent years, due to the

concern of lead poisoning from the resultant coatings, lithium hydroxide, sodium

hydroxide, or calcium oxide have been commonly used. The dosage of these cata-

lysts usually ranges from 0.01 to 0.06% metal based on the weight of the oil for lead

and 0.008 to 0.02% for lithium or calcium. The amount of catalyst added should be

kept at the minimum required for completing the reaction in an acceptable batch

time. They may cause poor color, poor water resistance, or haziness in the final

resin.

Ideally, 2 moles of polyol would react with 1 mole of triglyceride to form 3 moles

of monoester. In reality, the reaction would reach an equilibrium, whereby some

amount of diesters and triesters and neat polyol, including glycerol and the added

polyol, would coexist in the reaction mixture. The composition of the alcoholysis

product at equilibrium from soy oil and glycerol (1 : 2 mole ratio), and soy oil and

monopentaerythritol have been reported as follows (63):

Mole Percent

—————————————

Component Oil-Glycerol Oil-Mono-PE

Glycerol

Monoester 42 20.6

Diester 21 6.2

Triester 3 2.0

Free glycerol 33 14.0

PE

Monoester 29.0

Diester 16.8

Triester 5.1

Tetraester Negligible

Free PE 6.3


Diols, such as ethylene glycol, are usually not added during the alcoholysis step.

This is because their monoesters have only one remaining hydroxyl group and

would function as chain stoppers, thus severely limiting their utility in the structure

design of the resin molecules.

In general practice, the oil is first heated to 230–250�C under an inert gas blanket

and agitation. The catalyst, usually predispersed in a small quantity of the oil, and

the polyol, usually at 2 times the molar quantity of the oil present in the reactor, are

added. The batch is reheated to and maintained at the desired temperature, usually

in the 230–250�C range. The progress of the reaction is monitored by periodical

sampling from the reactor and checking miscibility with anhydrous methanol.

This is because triglycerides are not soluble in methanol, whereas monoglyceride

is. When a volume of the alcoholysate can tolerate three or more volumes of metha-

nol without becoming turbid, the alcoholysis process is considered complete.

Acidic contaminants are poisonous to the alcoholysis catalysts and must be

avoided. If the oil has a high acid number, or there are high acidity residues left

in the reactor from the previous batch, such as sublimed phthalic anhydride con-

densed under the dome of the reactor, the reaction can be severely retarded. A

longer batch time or additional amount of the catalyst would then be required.

Both are undesirable.

When the alcoholysis step is complete, the polybasic acid(s) and the balance of

polyol, if any, are added. The batch is reheated to and maintained at about 250�C to

carry out the polycondensation step to the desired endpoint, usually a combination

of the acid value and viscosity of the resin.

Fatty Acid Process. When free fatty acids are used instead of oil as the starting

component, the alcoholysis step is avoided. All of the ingredients can, therefore,

be charged into the reactor to start a batch. The reactants are heated together,

under agitation and inert blanket, until the desired end point is reached. Chen

and Kumanotani (64) reported that alkyds prepared by the fatty acid process

have narrower molecular weight distribution and give films with better dynamic-

mechanical properties.

A modified form of the fatty acid process, dubbed ‘‘high polymer alkyd tech-

nique’’ was reported (65). A portion of the fatty acids is withheld in the first stage

of the process to allow the polycondensation between the dibasic acid and the

polyol to have a better chance of extending the polyester chain without being termi-

nated by the monoacids. After the acid value of the reactant has reached a desired

low level, indicating the completion of the poly-condensation, the remaining

portion of fatty acids is then added to complete the process. The resins prepared

by this technique have more linear backbone chain structure, higher molecular

weight, and higher viscosity than the corresponding ones with identical formulation

but prepared by the conventional process.

Fatty Acid–Oil Process. When oil represents only a minor portion (33% or less)

of the total furnish of fatty acids in an alkyd formulation, the alcoholysis step may

be avoided. All of the ingredients, dibasic acid, polyol, oil, and free fatty acids may

be charged together into the reactor and proceed as in the fatty acid process. Appar-

ently, the oil is incorporated into the resin by ester interchange at the reaction

ALKYD RESINS 337

temperature. The resultant resins give higher viscosity (4), faster surface drying,

and slower through-dry (3). If the oil content is too high, not enough of it may

be incorporated in time, then it, would result in a partial gelation to form ‘‘seeds.’’

Acidolysis Process. As mentioned previously, isophthalic and terephthalic acids

are difficult to process in ordinary alkyd preparation methods, due to their high

melting point and low solubility in the reaction mixture. An acidolysis process

was developed for this purpose (6). The dibasic acid is heated together with the

oil in the resin formulation under agitation and inert gas blanket to about 280�C,

holding for about 40 min. In this reaction, which is self-catalyzed by the acidity

of the reaction mixture, an ester interchange occurs. A carboxyl group of the dibasic

acid displaces that of a fatty acid on the oil molecule and splits off the fatty acid.

The completeness of the acidolysis reaction is determined by a tedious extraction

of the oil phase and analysis of its free fatty acid content by titration. The analysis

takes several hours to complete. Rapid test methods, comparable to the methanol

miscibility test for alcoholysis, that could be used for process control of the acido-

lysis reaction have yet to be developed. Therefore, the process is normally con-

trolled by reaction time and temperature, based on experience. After acidolysis,

the reactant temperature is dropped to about 230�, the polyol is charged and heated

back up to the desired temperature to bring the esterification step to the desired

end point. The acidolysis process is not suitable for phthalic anhydride or other

dibasic acids with a high tendency to sublime.

Alkyd Resin Production Processes. Parallel to the above chemical procedures,

the processing method may also be varied with different mechanical arrangements

to remove by-product water, to drive the esterification reaction toward completion.

Fusion Process. In the fusion process, also frequently referred to as fusion cook,

inert gas is continuously sparged from the bottom of the reactor to carry away water

vapor from the reaction mixture. The exhaust is then either vented away or sent to a

fume scrubber, which is frequently a small vessel with water atomizing nozzles.

After the reaction is completed, the finished resin may be discharged, filtered,

and packaged without solvent. More frequently, it is cooled to a safe temperature,

then dissolved with the desired type and amount of solvent in a thinning tank, fil-

tered, and packaged, or pumped to a storage tank. The reactor usually needs to be

cleaned by charging a small volume of solvent into the vessel and heated to reflux

for an appropriate time period. If deemed necessary, the vessel is further cleaned

by digesting with caustic soda solution.

The fusion process has the advantage of simplicity in mechanical arrangement.

However, it has several significant disadvantages. Low boiling and/or subliming

ingredients, such as glycols and phthalic anhydride, would be lost during the reac-

tion causing the product composition and its properties to deviate from the design.

The material loss causes an increase in the cost of the resin. Reactants as well as the

product may adhere to the reactor walls above the surface level of the charge, which

will contaminate or even become catalyst poisons to the subsequent batches. And

the resin produced from a fusion cook is more prone to develop dark colors. For

these reasons, most of the manufacturers have discontinued the practice of fusion

cook, unless it is dictated by the existing equipment.


Solvent Process. In the solvent process, or solvent cook, the water formed from

the reaction is removed from the reactor as an azeotropic mixture with an added

solvent, typically xylene. Usually between 3 to 10 weight percent, based on the

total charge of the solvent, are added at the beginning of the esterification step.

The mixed vapor passes through a condenser. The condensed water and solvent

have low solubility in each other, and phase separation is allowed to occur in an

automatic decanter. The water is removed, usually to a measuring vessel. The

amount of water collected can be monitored as one of the indicators of the extent

of the reaction. The solvent is continuously returned to the reactor to be recycled. A

typical equipment for this process is shown in Figure 2. The reactor temperature is

Figure 2. Equipment for solvent processing of alkyd resins. Courtesy of Hercules Inc.

(Wilminton, Del.).

ALKYD RESINS 339

modulated by the amount and type of refluxing solvent. Typical conditions are as

follows.

The solvent vapor also serves as a blanket in the reactor. The processing solvent is

usually left in the product as part of the dilution solvent.

The refluxing solvent provides a constant wash to the reactor, and brings back

the reactants that had escaped out of the reaction mixture. The reaction temperature

is better controlled by the constant refluxing, and the viscosity of the reaction mix-

ture is lower, which improves the effectiveness of the agitation. The product usually

has better color and is more uniform than those made by the fusion process. Ordi-

narily, the reactor requires no more than a solvent wash to be clean enough for the

next batch. These advantages far outweigh the higher cost of the production facility.

Therefore, few would consider building a new alkyd plant without solvent process

capability.

When low boiling ingredients such as ethylene glycol are used, a special provi-

sion in the form of a partial condenser will be needed to return them back into the

reactor. Otherwise, not only would the balance of the reactants be upset and the raw

material cost of the resin be increased, they would also become part of the pollutant

in the waste water and incur additional water treatment costs. Usually, a vertical

reflux condenser or a packed column is used as the partial condenser, which is

installed between the reactor and the overhead total condenser (Figure 3). The

temperature in the partial condenser is monitored and maintained at a level to effect

a fractionation between water, which is to pass through the reactor, and the glycol

or other materials, which is to be condensed and returned to the reactor. If the frac-

tionation is poor and water vapor is also condensed and returned, the reaction will

be retarded and result in a loss of productivity. As the reaction proceeds toward

completion, water evolution slows down, and most of the glycol will have been

combined into the resin structure. The temperature in the partial condenser may

then be raised to facilitate the removal of water vapor.

5.9. Process Control

The progress of the alkyd reaction is usually monitored by periodical determina-

tions of the acid number and the viscosity (solution in a suitable solvent and at

an appropriate concentration) of samples taken from the reactor. The frequency

of sampling is commonly every half hour. The general practice is to plot the deter-

mined values separately against time on semilogarithmic coordinants (Figure 4).

Solvent Weight Percent Temperature (�C)

Xylene 3 251–260

Xylene 4 246–251

Xylene 7 204–210

High flash naphtha 10 204–210


Toward the end of the reaction, the resin viscosity tends to increase exponentially.

Gelation in the reactor is always a threat, due either to what the formulation would

theoretically allow by the completion of the polyesterification or to the occurrence

of some of the side reactions. After the onset of gelation, it would progress extre-

mely rapidly and would be almost impossible to arrest. Therefore, it is routine to

Figure 3. Solvent-processing equipment using a partial condenser. Courtesy of Hercules Inc.

(Wilmington, Del.).

ALKYD RESINS 341

extrapolate the plots in Figure 4 when predicting the point at which to terminate the

reaction in time to prevent gelation. If gelation should occur in the reactor, it would

cause not only the loss of product but also significant down time for cleaning the

reactor. Some alkyd practitioners have found that a rapid addition of a large quan-

tity of raw oil quenches the runaway gelation, disperses the gel, and significantly

eases the cleanup operation. A technique of injecting water or steam during the

condensation process to reverse or retard gelation has been reported in the patent

literature (66).

Figure 4. Alkyd reaction control plots.


6. SAFETY AND ENVIRONMENTAL PRECAUTIONS

The manufacturing of alkyd resins involves a wide variety of organic ingredients.

While most of them are relatively mild with low toxicity, some of them such as

phthalic anhydride, maleic anhydride, solvents, and many of the vinyl (especially

acrylic) monomers are known irritants, or skin sensitizers, and are poisonous to

humans. Persons involved should be thoroughly familiar with the hazard potential

of each and every one of the chemicals by consulting the material safety data sheets

provided by the suppliers and practicing the recommended safety precautions in

handling the materials. The use of personal safety equipment such as protective

goggles, gloves, clothing, and respiratory devices should be diligently observed.

Since large quantities of highly flammable solvents are routinely handled in an

alkyd plant, fire safety should be the utmost in everyone’s mind. Electrical equip-

ment and power circuitry in the plant should conform to all applicable codes, and

all equipment should be properly grounded. The areas for the reactors and storage

tanks should be separated by fire walls and must be adequately ventilated. The

storage tanks should be blanketed by inert gas. A slight positive pressure of inert

gas should be maintained in the reactor or storage tanks during discharge of the

resin or resin solution to prevent air from being sucked into the vessel to form

an explosive mixture with the solvent vapor.

With the ever increasing awareness of the need for environmental protection,

the emission of solvent vapors and organic fumes into the atmosphere should be

prevented by passing the exhaust through a proper scrubber. The solvent used for

cleaning the reactor is usually consumed as part of the thinning solvent. Aqueous

effluent should be properly treated before discharge.

7. MODIFICATION OF ALKYD RESINS BY BLENDINGWITH OTHER POLYMERS

As mentioned earlier, one of the important attributes of alkyds is their good com-

patibility with a wide variety of other coating polymers. This good compatibility

comes from the relatively low molecular weight of the alkyds and the fact that the

resin structure contains, on the one hand, a relatively polar and aromatic backbone

and, on the other hand, many aliphatic side chains with low polarity. The alkyd

resin involved in a blend with another coating polymer may serve as a modifier

for the other film former, or it may be the major film former and the other polymer

may serve as the modifier for the alkyd to enhance certain properties. The following

describes some of these compatible blends.

Nitrocellulose-based lacquers often contain a fair amount of short- or medium-

oil alkyds to improve flexibility and adhesion. The most commonly used are

short-oil nondrying alkyds. Amino resins or urethane resins with residual isocya-

nate functional groups may be added to cross-link the coating film for improved

MODIFICATION OF ALKYD RESINS BY BLENDING WITH OTHER POLYMERS 343

solvent and chemical resistance. The major applications are furniture coatings, top

lacquer for printed paper, and automotive refinishing primers.

Amino resins are probably the most important modifiers for alkyd resins. Butyl-

ated urea- or melamine–formaldehyde resins are compatible with alkyds. They

react with the free hydroxyl groups of the alkyd to effect cross-linking and to impart

hardness, mar resistance, chemical resistance, and durability to the coating. Short-

or medium-oil alkyds of both drying and nondrying types are frequently used. Color

and color retention requirements often dominate the choice of the alkyd. Many

industrial baking enamels, such as those for appliances, coil coatings, and auto-

motive finishes (especially refinishing enamels), are based on alkyd-amino resin

blends. Some of the so-called catalyzed lacquers for finishing wood substrate

require low bake or no bake at all.

Chlorinated rubber is often used in combination with medium-oil drying type

alkyds. The alkyd gives better toughness, flexibility, adhesion, and durability, and

the chlorinated rubber contributes to faster dry and better resistance to water

and chemicals. The major applications are highway traffic paint, concrete floor,

and swimming pool paints.

Vinyl resins of the type that are the copolymers of vinyl chloride and vinyl acet-

ate and that contain a fair amount of hydroxyl groups (from the partial hydrolysis of

vinyl acetate) and/or carboxyl groups (e.g., from copolymerized maleic anhydride)

may be formulated with alkyd resins to improve application properties and adhe-

sion. The blends are primarily used in making marine topcoat paints.

Synthetic latex house paints sometimes contain emulsified long-oil or very long

oil drying alkyds to improve adhesion to chalky painted surfaces.

Silicone resins with high phenyl contents may be used with medium- or short-oil

alkyds as blends in air-dried or baked coatings to improve heat and weather resis-

tance, whereas the alkyd component contributes to adhesion and flexibility. Major

applications include insulation varnishes, heat-resistant paints, and marine coatings.

7.1. Chemically Modified Alkyd Resins

While blending with other coating resins provides a variety of ways to improve the

performance of alkyds, or vice versa, chemically combining the desired modifier

into the alkyd structure would eliminate the compatibility problem and give a more

uniform product. Several such chemical modifications of the alkyd resins have

gained commercial importance, and are described below.

Vinylated alkyds are alkyd resins that have been incorporated with a significant

amount (20–60% by weight) of vinyl monomers (such as styrene, vinyl toluene, and

methyl methacrylate) by grafting the monomers through a free-radical mechanism

onto unsaturated reaction sites in the resin molecules. The modified resin embodies

the good attributes of ease of application, good wetting, and adhesion from the

alkyd as well as fast solvent release, hardness, and weather resistance from the vinyl

modification. The common objective of such a modification is for achieving a

drying rate comparable to that of lacquer materials. The reaction sites on alkyd

resin molecules are primarily the allylic carbons on unsaturated fatty acid chains


and the double bond of a,b-unsaturated dibasic acids. Free radicals, generated from

the thermolysis of such free-radical initiators as benzoyl peroxide, dicumyl perox-

ide, and di-t-butyl peroxide are usually required to kick off the reaction. Ideally, the

initiating species would attack the active sites on the resin molecules and all of the

added monomers would be evenly distributed in grafted side chains. In reality, it is

inevitable that part of the monomers would engage in homopolymerization, and

some of the resin molecules would remain unmodified. The presence of a large

amount and high molecular weight homopolymer of the vinyl monomer would

lead to incompatibility and result in a hazy product. Methods that have been

used to minimize homopolymerization include using fatty acids having conjugated

diene structure, using maleic anhydride as part of the dibasic acids for the alkyd,

choosing initiators such as peroxides or hydroperoxides that tend more to extract

allylic protons than to add to double bonds, avoiding initiators that would decom-

pose at very low temperatures, adding the monomer gradually along with an appro-

priate amount of the initiator, choosing monomers that would have a more

favorable tendency to copolymerize with the active species on the alkyd resin,

and properly maintaining the reaction temperature. Chain transferring is the pre-

ferred mechanism for terminating chain growth from the addition polymerization

of the monomer. Usually, the solvent, the fatty acid chain, and the monomer are

effective chain-transfer agents. If an additional transferring agent is used, care

must be exercised, or too much of it could cause the formation of a large amount

of very low molecular weight homopolymers, and would result in poor film proper-

ties. Occasionally, vinylation is first performed on the fatty acids or the oil before

the alkyd reactions.

It should be emphasized that the presence of a large amount of either conjugated

fatty acids or maleic anhydride in the alkyd formulation gives rise to a high degree

of probability of premature gelation during the alkyd reaction. An allowance must

be made in the alkyd formulation, and the polyesterification is frequently termi-

nated at a relatively high acid number (about 15), to avoid gelation. It has been

reported that the optimum amount of maleic anhydride in the alkyd is an amount

having a maleic group in one-third of the resin molecules (17).

A common procedure for the preparation of vinylated alkyds is as follows: first,

a base alkyd resin is brought to the desired end point. The resin is then cooled to

about 160�C and often diluted with aromatic thinner. Next, the desired monomer is

added, usually at about 20–60% based on the final product, followed by an appro-

priate amount of a free-radical initiator. Alternatively, a premix of the monomer and

the initiator is added at a controlled rate over most of the reaction. Then the reaction

is brought to monomer reflux, until the residual monomer content has dropped

below a specified level. The residual monomer, if any, is stripped away before the

product is diluted in a solvent, filtered, and packaged.

Silicone alkyds are etherification products of alkoxy-polysiloxane oligomers

and the free hydroxyl groups of alkyd resins (67, 68). The property improvements

and applications are similar to those of the alkyd-silicone blends, with the added

advantage of incorporating the stable ��Si��O��C�� structure into the alkyd mole-

cules. The preferred silicone oligomers are those with high phenyl contents, and


the alkyds at long- or medium-oil length based on polyols with primary hydroxyls.

To improve the thermal stability effect imparted by the silicone modification

further, one can use isophthalic alkyds rather than the phthalic type. The etherifica-

tion reaction may be carried out on an alkyd resin designed for the purpose or on the

polyol before it is used in alkyd preparation. The silicone content of the modified

alkyd lies usually between 20 and 60% of the total product.

Urethane alkyds, or uralkyds, are alkyds with a part or even all of the dibasic

acids replaced by diisocyanates. The isocyanate group, ��N��C��O, reacts with

the hydroxyl group of a polyol, at low temperature, to form a urethane linkage,

��NHC(O)O��, without spitting out water as a by-product. Toluene diisocyanate

(TDI) is commonly used for such modification. It is commercially supplied as an

80 : 20 mixture of 2,4- and 2,6-isomers. The ��NCO� group para to the methyl

group has about 8 times greater reactivity than the one on the ortho position, which

aids greatly the control of the reaction. Since the NCO group is reactive with labile

protons, water must be excluded from the reaction system. The esterification reac-

tion of the base alkyd must be brought to the desired end point with the by-product

water removed, and the temperature lowered to about 100�C to prevent any conti-

nuation of the esterification before the introduction of the NCO reactant. TDI is

highly toxic and is usually handled in a closed system under a dry inert gas blanket.

Metallic soaps, such as dibutyltin dilaurate, stannous octoate, and calcium naphtha-

nate, are used as reaction catalysts. The reaction is vigorous and exothermic. There-

fore, the reaction temperature is maintained under 135�C, and great care must be

exercised to bring the reaction under proper control.

Uralkyds have superior adhesion, hardness, abrasion resistance, durability, and

chemical resistance to the unmodified alkyds. They find major applications in wood

floor finishes, marine coatings, metal primers, and maintenance paints.

Phenolic resins are well known for their contribution in improving hardness,

gloss, and water and chemical resistance in oleoresinous varnishes. Those based

on p-alkyl-substituted phenols and with heat-reactive methylol groups have also

been incorporated into alkyd resins. The reaction has not been well studied. Pre-

sumably, the methylol group would react with the unsaturation functionality on

the fatty acid chain to form the chroman structure, similar to what is believed to

have occurred in the varnish. Etherification between the methylol group and free

hydroxyl of the alkyd resin, catalyzed by the residual acidity in the resin, would

be another possible reaction.

Polyamide modified alkyds show a special rheological behavior—they are thix-

otropic (69, 70). Typically, the polyamide resin would be of the type based on dimer

acids, i.e., dimerized unsaturated fatty acids, and aliphatic diamines, such as ethy-

lene diamine. These would react to form polyamide resins with low acid and amine

values. The alkyd resin would be a medium- or long-oil drying alkyd. The reaction

products from the polyamide and the alkyd are gel-like materials that undergo a

time-dependent shear thinning and recover to the gel-like state after the shearing

action is stopped. This allows the preparation of ‘‘no-drip’’ paints, which are

easy to brush and can be applied at high film thickness from a single coat with little

or no danger of sagging. Pigment settling during storage of the paint is also


minimized. The major applications are flat oil-based architectural paints and main-

tenance paints. Generally, up to 10% of the polyamide based on the weight of the

alkyd is added to the alkyd and heated at normal alkyd reaction temperature under

agitation. Ester interchange reaction takes place, and fragments of the polyamide

resin become chemically bonded to the alkyd. The modified alkyd serves as a com-

patibilizer for the mutually insoluble unreacted polyamide and alkyd to form a

gellike structure. The stiffness of the structure decreases with the increasing amount

of the compatibilizer. If the reaction is allowed to continue, and there is no unreact-

ed polyamide left in the system, little or no thixotropy will be exhibited. Therefore,

the reaction must be precisely controlled to give the desired degree of thixotropy.

Aromatic solvents such as xylene tend to destroy the thixotropic structure. There-

fore, they must be reduced to less than 0.5% in the product. Polyamide modified

alkyd resins are available commercially to be used as additives for making thixotro-

pic alkyd paints.

7.2. High Solids Alkyds

There has been a strong trend in recent years to increase the solids level of all coat-

ing materials, including alkyds, to reduce solvent vapor emission. To raise the

solids level and still maintain a manageable viscosity, the molecular weight of

the resin must be reduced. Consequently, film integrity must be developed through

further chain extension and/or cross-linking of the resin molecules during the ‘‘dry-

ing’’ step. A high cross-linking density necessitated by the lower molecular weight

of the resin would build a high level of stress in the film, and cause it to be prone to

cracking. Therefore, adequate flexibility should be designed into the resin structure.

This means that the distance between the hydroxyl groups of the polyol and the

carboxyl groups of the dibasic acid would need to be lengthened by linear linkages.

Thus long-chain diols, polyether polyols, and linear a,o-dibasic acids would not

only build in more flexibility but also reduce the viscosity for high solids alkyds,

due to the greater spacing of polar ester groups and the reduction of aromaticity in

the resin structure. In addition to the manipulation of resin molecular structure for

increasing coating solids, the use of more active, though more expensive, oxyge-

nated solvents also serves to reduce the viscosity of resin solutions.

Chain extension and cross-linking of high solids alkyd resins are typically

achieved by the use of polyisocyanato oligomers or amino resins. An adequate

amount of excess hydroxyl groups must be designed into the alkyd structure to

provide reaction sites for these modifiers. To limit the molecular weight of the alkyd

resin, the molar ratio between polyols and dibasic acids should be greater than 1.

The hydroxyl functionality of the formulation should be controlled by a careful

selection of polyols to avoid an overpresence of free hydroxyl groups in the pro-

duct, which would adversely affect water resistance and other properties of the

coating film. Most of the high solids alkyd systems are used in industrial baking

finishes. For air drying applications, higher doses of driers are usually needed to

achieve acceptable drying rate (71).


7.3. Water-Reducible Alkyds

Replacing solvent-borne coatings with water-borne coatings would not only reduce

solvent vapor emission but also improve safety against the fire and health hazards of

organic solvents. Alkyd resins may be rendered water-reducible by either convert-

ing the resin into an emulsion form or by incorporating ‘‘water-soluble’’ groups in

the molecules. The latter will be the subject for further discussion.

The most common approach for imparting water solubility in an alkyd resin is to

leave enough pendent carboxyl groups in the resin and to neutralize them with a

fugitive base, such as ammonia or low molecular weight amines, to build ionic char-

acteristics into the resin. Nonfugitive base materials, such as caustic soda, would

leave the salt in the coating film and damage its water- and corrosion-resistance.

Trimellitic anhydride (TMA) is the most frequent choice of ingredient to provide

the pendent carboxyl groups. It was reported that glycerol gives resins with poor

hydrolytic stability (72). Therefore, polyols with primary hydroxyl groups are pre-

ferred for the preparation of water-soluble alkyds.

The recommended procedure (37) for the preparation of water-soluble alkyds is

to hold off the TMA in the initial stage of the alkyd reaction so that the high func-

tionality of TMA would not be a cause of gelation. When the reaction has pro-

gressed to a desired low acid number, i.e., the building of the polymer chain is

completed, the temperature is lowered to 180�C; the TMA is then added and main-

tained at that temperature until a desired acid number, usually about 50–60, is

reached. At such a temperature, only the anhydride group of the TMA would react

to form half esters, and the remaining two carboxyl groups would essentially

remain unreacted. If one desires to have the TMA participating in the backbone

structure of the resin, a part of the TMA is charged in the beginning of the alkyd

reaction, often with the presence of an appropriate amount of a monohydric alcohol,

such as benzyl alcohol, to balance the functionality of the system. The remaining

TMA is then added in the same manner as described to ‘‘end cap’’ the resin and to

provide pendent carboxyl groups for water solubilization.

The finished resins are usually dissolved in oxygenated coupling solvents, such

as glycol ethers, to improve the solubilization of the resin in aqueous media and the

handling of the resin. Water and the base are premixed and added to the resin solu-

tion when needed. The coupling solvents usually have higher boiling points than

water. During the drying process, the solvent would be enriched in the coating

film as water evaporates preferentially. The resin molecules would become better

solubilized, i.e., molecular chains would be extended, and result in better formation

and integrity of the film.

8. ECONOMIC ASPECTS

Alkyd resins as a family have remained the workhorse of the coatings industry for

decades. In the United States, the total consumption of alkyds increased from about

200,000 t in the mid-1950s to more than 300,000 t in the mid-1960s. It peaked in


1973 at about 345,000 t, constituting about 33% of all synthetic coating resins.

In 1980, alkyds still accounted for 30% of the 1,090,000 t of all resins consumed

for coatings. From 1987 to 1989, although the consumption maintained at about

300,000 t/year, its market share among all coating resins was reduced to 26% in

1987 and 25% in 1989. At present, 55–60% of the alkyd resins consumed in the

United States are used for architectural coatings. A decline in consumption is

expected because of regulations involving VOCs (volatile organic emissions). Cali-

fornia and the Northeastern United States are expected to adopt regulations that will

severely restrict the use of solvent-borne coatings (73).

The overall demand in Europe is expected to decrease at the rate of 3%/yr over

the next five years. Environmental regulations are expected by 2007. Japan’s con-

sumption has declined, but has stabilized because high performance alternatives

have already replaced the coatings in question.

The industry was hard hit in 2003–2004 with higher prices for raw materials

such as linseed and soybean oil. Alkyd producers are already developing new

water-borne products (73).

Other uses for alkyds are in general industrial coatings such as machinery and

metal furniture. Alkyd resin-chlorinated rubber based coatings are used in traffic

paints, but use is declining because of VOC concerns. Some alkyds are still used

in refinish paints for automobiles. Uralkyds are used as a vehicle for urethane

varnishes for the do-it-yourself market.

9. FUTURE PROSPECTS

Stemming from the drive by the coatings industry to reduce solvent emission, there

has been a clear trend of gradual decline in the market share of alkyd resins. How-

ever, their versatility and low cost will undoubtedly continue to keep alkyds as

major players in the coatings arena. Alkyds are much more amenable to move to-

ward higher solids than most other coating resins. Great strides in the development

of water-borne types have also been made in recent years. There is one more good

reason to remain optimistic about alkyds for the future—a significant portion of

their raw material, fatty acids, is renewable.

REFERENCES

1. A. E. Rheineck, J. Paint Technol. 44(566), 35–54 Apr. 1972.

2. A History of Paint and Color, Pittsburgh Plate Glass Co., 1951.

3. An Overview of the Paint and Coatings Industry, SRI International, Aug. 1992.

4. D. Deffar and M. D. Soucek, J. Coat. Technol, 73 (919), 95 (2001).

5. Urethane Surface Coatings, SRI Consulting, Oct. 2004.

6. Epoxy Surface Coatings, SRI Consulting, Oct. 2004.

7. Z. W. Wicks, Jr. and F. N. Jones in Z. W. Wicks, F. N. Jones, and S. P. Pappas, eds., Organic

Coatings Science & Technology, Vol. 1, John Wiley & Sons, Inc., New York, 1992, Chapt. 9.

REFERENCES 349

8. A. E. Rheineck and R. O. Austin in R. R. Meyers and J. S. Long, eds., Treatise on

Coatings, Vol. 1, Part 2, Marcel Dekker, Inc., New York, 1968, Chap. 4.

9. D. N. Rampley and J. A. Hasnip, J. Oil Colour Chem. Assoc. 59, 356–362 (1976).

10. O. S. Privett, W. O. Lundberg, N. A. Khan, W. E. Tolberg, and D. H. Wheeler, J. Am. Oil

Chem. Soc. 30, 61, (1953).

11. S. A. Harrison and D. H. Wheeler, J. Am. Chem. Soc. 76, 2379 (1954).

12. O. S. Privett and C. J. Nickell, J. Am. Oil Chem. Soc. 33, 156 (1956).

13. W. J. Bailey and G. L. Barlow, J. Paint Technol. 42(544), 287 (1970).

14. E. H. Farmer and A. Sundralingam, J. Chem. Soc. 1942, 121.

15. E. H. Farmer and D. A. Sutton, J. Chem. Soc. 1942, 139.

16. J. L. Bolland and G. Gee, Trans. Faraday Soc. 42, 236, 244 (1946).

17. E. H. Farmer, Trans. Faraday Soc. 42, 228 (1946).

18. E. H. Farmer, Trans. Inst. Rubber Ind. 21, 122 (1945).

19. F. D. Gunstone and T. P. Hilditch, J. Chem. Soc. 1946, 1022.

20. N. A. Khan, Can. J. Chem. 32, 1149 (1954).

21. N. Uri in W. O. Lunberg, ed., Autoxidation and Antioxidants, Vol. 1, Wiley-Interscience,

New York, 1961, Chapt. 2.

22. F. W. Heaton and N. Uri, J. Lipid Res. 2, 152 (1961).

23. T. H. Smouse and S. S. Chang, J. Am. Oil Chem. Soc. 44, 509 (1967).

24. H. P. Kaufmann, Fette Seifen Anstrichmit. 59, 153–162 (1957).

25. O. S. Privett, J. Am. Oil Chem. Soc. 36, 507 (1959).

26. R. N. Faulkner, J. Appl. Chem. 8, 448–458 (1958).

27. R. R. Allen and F. A. Kummerow, J. Am. Oil Chem. Soc. 28, 101 (1951).

28. A. E. Rheineck and S. C. G. Peng, Official Digest 36, 878 (1964).

29. L. A. O’Neill, Chem. Ind. 1954, 384–387.

30. K. Hultzsch, J. Prakt. Chem. 158, 275 (1941).

31. R. H. Kienle and C. S. Ferguson, Ind. Eng. Chem. 21, 349 (1929).

32. R. H. Kienle, Ind. Eng. Chem. 41, 726 (1949).

33. R. G. Mraz and R. P. Silver in Encyclopedia of Chemical Technology, 2nd ed., Vol. 1, John

Wiley & Sons, Inc., New York, 1963, pp. 851–880.

34. Z. W. Wicks, Jr., in Encyclopedia of Chemical Technology, 5th ed., Vol. 2, John Wiley &

Sons, Inc., Hoboken, New Jersey, 2004, pp. 147–169.

35. C-D-I-C Society for Paint Technology, Official Digest 430, 1477 (Nov. 1960).

36. Bulletin IP4, Amoco Chemicals Corp., Chicago, Oct. 1960.

37. Bulletin IP-65b, Amoco Chemicals Corp., Chicago, 1990.

38. Technical Bulletin No. 524-5, Velsicol Chemical Corp., Chicago.

39. R. I. Stirton in Encyclopedia of Chemical Technology, 1st ed., p. 595, Interscience

Publishers, New York, 1953.

40. Bulletin TMA 27, Amoco Chemicals Corp., Chicago.

41. IMC Polyols: A Complete Guide, International Minerals & Chemicals Corp., Des Plaines,

Ill., 1980, p. 9.

42. Trimethylolpropane in Alkyd Coating Resins, Celanese Chemical Co., New York, 1961, p. 4.


43. L. Klee and G. H. Benham, J. Am. Oil Chem. Soc. 27, 130–133 (1950).

44. A. E. Rheineck, F. D. Williamson, and D. DeClerk, Am. Chem. Soc. Div. Org. Coat. Plast.

Chem. 22(1), 24–34 (1962).

45. W. H. Carothers, J. Am. Chem. Soc. 51, 1548 (1929).

46. P. J. Flory, Principles of Polymer Chemistry, Cornell University Press, Ithaca, N.Y., 1953,

Chapt. 9.

47. W. H. Carothers, Trans Faraday Soc. 32, 43 (1936).

48. T. C. Patton, Alkyd Resin Technology, Formulating Techniques and Allied Calculations,

Wiley Interscience, New York, 1962.

49. E. G. Bobalek, E. R. Moore, S. S. Levy, and C. C. Lee, J. Appl. Polym. Sci. 8, 625–657

(1964).

50. D. H. Solomon, B. C. Loft, and J. D. Swift, J. Appl. Polym. Sci. 11, 1593–1602 (1967).

51. D. H. Solomon and J. J. Hopwood, J. Appl. Polym. Sci. 10, 1893–1914 (1966).

52. J. Kumanotani, H. Hata, and H. Masuda, Org. Coat. 6, 35–54 (1984).

53. H. Kiryu, K. Horiuchi, K. Sato, and J. Kumanotani, Shikizai Kyokaishi 57(11), 597–601

(1984).

54. H. Hata, H. Tomita, Y. Nishizawa, and J. Kumanotani, Fatipec Cong. 15(3), 111-485/509

(1980).

55. H. Hata, J. Kumanotani, Y. Nishizawa, and H. Tomita, Fatipec Cong. 14, 359–364 (1978).

56. N. M. Wiederhorn, Am. Paint J. 41(2), 106 (1956).

57. R. P. Silver, Alkyd Report No. 8, Hercules Inc., Wilmington, Del.

58. R. P. Silver, Alkyd Report No. 1.2, Hercules Inc., Wilmington, Del.

59. T. C. Patton, Off. Digest Fed. Paint Varnish Prod. Clubs 430, 1544 (1960).

60. Y. Tanizaki and T. Yoshida, Shikizai Kyokaishi 45(2), 83–87 (1972).

61. T. Nagata, J. Appl. Polym. Sci. 13, 2601–2619 (1969).

62. T. Yoshida, Kobunshi Kagagu 22, 769 (1965).

63. Alkyd Report No. 1.5, Hercules Inc., Wilmington, Del.

64. L. W. Chen and J. Kumanotani, J. Appl. Polym. Sci. 9, 3649–3660 (1965).

65. W. M. Kraft, G. T. Roberts, E. G. Janusz, and J. Weisfeld, Am. Paint J. 41(28), 96 (1957).

66. W. B. Callahan and B. F. Coe (to E. I. du Pont de Nemours & Co.), U.S. 4,045,932

(Aug. 30, 1977).

67. A. F. Karim, B. Golding, and R. A. Morgan, J. Chem. Eng. Data 5, 117 (1960).

68. Silicone Notes 7-701, 7-702a, 7-703, Technical Bulletin, Dow Corning Corp., Midland,

Mich.

69. A. G. North, J. Oil Color Chem. Assoc. 39(9), 696 (1956).

70. P. Oldring and G. Hayward, eds., Resins for Surface Coatings, SITATechnology, London,

1987.

71. J. Larson, Am. Paint Coat. J., 56–61 (Apr. 4, 1984).

72. M. Lerman, J. Coat. Technol. 48(12), 37–42 (1976).

73. Alkyd/Polyester Surface Coatings, SRI Consulting, Jan. 2005.

REFERENCES 351

Alkyd Drying

Documents

double bonds

industrial

coating applications

raw materials

drying nishes

drying characteristics

protective

drying oil